Optical disk, method for recording and reproducing write-once information on and from optical disk, optical disk reproducing device, optical disk recording and reproducing device, device for recording write-once information on optical disk, and optical disk recording device

ABSTRACT

An optical disk storing write-once information usable for protecting the copyright of the software by preventing the duplication, unauthorized use, etc., of the software. In the optical disk, a recording layer ( 213 ) is formed on a disk substrate ( 211 ) with a dielectric layer ( 212 ) inbetween. Then, an intermediate dielectric layer ( 214 ) and a reflecting layer ( 215 ) are successively laminated upon the recording layer ( 213 ), and an overcoat layer ( 216 ) is formed on the surface of the reflecting layer ( 215 ). A plurality of BCA (one of write-once identification information systems) sections ( 220   a  and  220   b ) are recorded by lowering the vertical magnetic anisotropy of the recording layer ( 213 ). At the time of reproduction, the write-once information is detected from differential signals.

FIELD OF THE INVENTION

[0001] The present invention relates to an optical disk for recording,reproducing and erasing information. In particular, the presentinvention relates to an optical disk comprising write-once informationthat can be used for copyright protection, for example forcopy-protection or protection from unauthorized use of software.Throughout this specification, “write-once information” refers toinformation that is recorded after finishing the disk manufacturingprocess. The present invention relates further to a method for recordingand a method for reproducing write-once information on the optical disk,an apparatus for reproducing the optical disk, an apparatus forrecording and reproducing the optical disk, an apparatus for recordingwrite-once information on the optical disk, and an apparatus forrecording on the optical disk.

BACKGROUND OF THE INVENTION

[0002] In recent years, the speed with which electronic calculators andinformation processing systems can process ever greater amounts ofinformation has increased sharply. Together with the digitalization ofaudio and video information, this gave rise to the rapid disseminationof low-cost, high-volume auxiliary storage devices and recording mediatherefor, especially optical disks, which can be accessed with highaccess speeds.

[0003] The basic configuration of conventional optical disks is asfollows: A dielectric layer is formed on top of a disk substrate, and arecording layer is formed on top of the dielectric layer. On top of therecording layer, an intermediate dielectric layer and a reflecting layerare formed in that order. An overcoat layer is formed on top of thereflecting layer.

[0004] The following is an explanation of how an optical disk with theabove configuration is operated.

[0005] In the case of an optical disk having, in its recording layer, amagneto-optical layer with perpendicular magnetic anisotropy, therecording and erasing of information is performed by locally (a) heatingthe recording layer with a laser beam to a temperature with smallcoercive force above the compensation temperature or to a temperaturenear or above the Curie temperature to decrease the coercive force ofthe recording layer in the irradiated portion, and (b) magnetizing therecording layer in the direction of an external magnetic field. (This isalso called “thermomagnetic recording” of information.). Moreover, forthe reproduction of the recording signal, a laser beam with lessintensity than the laser beam for recording or erasing irradiates therecording layer. The recording state of the recording layer, that is,the rotation of the polarization plane of the light that is reflected ortransmitted in accordance with the orientation of the magnetic field(this rotation occurs mainly due to two magneto-optical effects—the Kerreffect and the Faraday effect), is detected by a photodetector throughthe change in the intensity of the irradiated light. In order todecrease the interference between opposite magnetizations and allowhigh-density recordings, a magnetic material with perpendicular magneticanisotropy is used for the recording layer of the optical disk.

[0006] Moreover, when the data is reproduced, the reproduction signallevel during data reproduction can be raised to detect the reproductionsignal by using a layered structure for the recording layer: Severalmagnetic thin films comprising an exchange coupling multilayer or amagneto-static coupling multilayer.

[0007] For the recording layer, a material is used that can recordinformation by locally raising the temperature or inducing a chemicalreaction due to absorption of the irradiated laser light. The localvariations in the recording layer can be detected by irradiating laserlight of a different intensity or wavelength than that used for therecording and detecting the reproduction signal using the reflected orthe transmitted light.

[0008] Regarding such optical disks, there is a need for a way toprotect the data on the disk with write-once information (identificationdata) that allows for copyright protection, for example copy protectionand protection against unauthorized use of software.

[0009] With the above configuration, it is possible to record diskinformation in TOC (or control data) areas, but when disk data isrecorded with pre-pits, the disk information has to be administeredstamper by stamper and cannot be administered user by user.

[0010] Moreover, when information is recorded using a magnetic film or afilm of a phase-reversible material, administrative information easilycan be changed, which means that it easily can be rewritten(manipulated), so that the contents on the optical disk cannot becopyright protected.

SUMMARY OF THE INVENTION

[0011] It is an object of the present invention to solve the problems ofthe prior art. It is a further object of the present invention toprovide an optical disk comprising write-once information that can beused for copyright protection, for example for copy-protection orprotection from unauthorized use of software, a method for recordingwrite-once information on an optical disk, a method for reproducingwrite-once information from an optical disk, an apparatus forreproducing optical disks, an apparatus for recording and reproducingoptical disks, an apparatus for recording write-once information onoptical disks, and an apparatus for recording on optical disks.

[0012] In order to attain these objects, a first configuration of anoptical disk in accordance with the present invention comprises a disksubstrate and a recording layer on the disk substrate. The recordinglayer includes a magnetic film with a magnetic anisotropy in a directionperpendicular to a surface of the magnetic film. The optical disk storeswrite-once information formed by first recording areas and secondrecording areas in a predetermined portion of the recording layer. Amagnetic anisotropy in a direction perpendicular to a surface of thesecond recording areas is smaller than a magnetic anisotropy in adirection perpendicular to a surface of the first recording areas. Thesecond recording areas are formed as stripe-shaped marks that are oblongin a radial direction of the disk. A plurality of the marks is arrangedin a circumferential direction of the disk, the arrangement being basedon a modulation signal of the write-once information. In accordance withthis first configuration, an optical disk can be achieved, whichcomprises write-once information that can be used for copyrightprotection, for example for copy-protection or protection fromunauthorized use of software.

[0013] It is preferable that the optical disk according to the firstconfiguration further comprises an identifier indicating whether thereis a row of a plurality of marks arranged in a circumferential directionof the disk. With this configuration, the system can be started in ashort time. Moreover, in this configuration, it is preferable that theidentifier indicating the row of marks is stored among control data.With this configuration, it is known when the control data is reproducedwhether write-once information is stored, so that the write-onceinformation can be reproduced reliably.

[0014] It is preferable that in the optical disk according to the firstconfiguration, the pre-determined portion comprising write-onceinformation is at an inner perimeter portion of the disk. With thisconfiguration, the position of the optical head with respect to a radialdirection of the disk can be determined with an optical head stopper oraddress information of a bit signal.

[0015] It is preferable that in the optical disk according to the firstconfiguration, a difference between a luminous energy that is reflectedfrom the first recording areas and a luminous energy that is reflectedfrom the second recording areas is below a certain value. It isparticularly preferable that the difference between luminous energy thatis reflected from the first recording areas and luminous energy that isreflected from the second recording areas is not more than 10%. Withthis configuration, variations of the reproduction waveform accompanyingchanges of the reflected luminous energy can be suppressed.

[0016] It is preferable that in the optical disk according to the firstconfiguration, a difference between an average refractive index of thefirst recording areas and an average refractive index of the secondrecording areas is not more than 5%. With this configuration, thedifference between luminous energy that is reflected from the firstrecording areas and luminous energy that is reflected from the secondrecording areas can be adjusted to not more than 10%.

[0017] It is preferable that in the optical disk according to the firstconfiguration, the magnetic anisotropy of the magnetic film of thesecond recording areas in an in-plane direction is dominant. With thisconfiguration, using a reading device having a polarizer and aphotodetector the reproduction signal of the first recording areas,which corresponds to the write-once information, can be attained. Thus,the write-once information can be obtained rapidly and without using anoptical head.

[0018] It is preferable that in the optical disk according to the firstconfiguration, at least a portion of the magnetic film of the secondrecording areas is crystallized. With this configuration, the magneticanisotropy perpendicular to the magnetic film of the second recordingareas can be almost completely eliminated, so that the reproductionsignal can be reliably detected as the difference of the polarizationorientation to the first recording areas.

[0019] It is preferable that in the optical disk according to the firstconfiguration, the recording layer comprises a multilayer magnetic film.With this configuration, the magnetically induced super resolutionmethod “FAD” can be used as the reproduction method. Thus, signalreproduction with regions smaller than the laser beam spot becomespossible.

[0020] A second configuration of an optical disk in accordance with thepresent invention comprises a disk substrate and a recording layer onthe disk substrate. The recording layer includes a film that can bereversibly changed between two optically detectable states. The opticaldisk stores write-once information formed by first recording areas andsecond recording areas in a pre-determined portion of the recordinglayer. A luminous energy that is reflected from the first recordingareas differs from a luminous energy that is reflected from the secondrecording areas. The second recording areas are formed as stripe-shapedmarks that are oblong in a radial direction of the disk. A plurality ofthe marks is arranged in a circumferential direction of the disk, thearrangement being based on a modulation signal for the write-onceinformation. In accordance with this second configuration, an opticaldisk can be achieved, which comprises write-once information that can beused for copyright protection, for example for copy-protection orprotection from unauthorized use of software.

[0021] It is preferable that the optical disk according to the firstconfiguration further comprises an identifier for indicating whetherthere is a row of a plurality of marks arranged in a circumferentialdirection of the disk. Moreover, it is preferable that the identifierindicating the row of marks is stored among control data.

[0022] It is preferable that in the optical disk according to the firstconfiguration, the pre-determined portion comprising write-onceinformation is at an inner perimeter portion of the disk.

[0023] It is preferable that in the optical disk according to the firstconfiguration, the recording layer undergoes a reversible phase changebetween a crystalline phase and an amorphous phase, depending onirradiation conditions for irradiated light. With this configuration,information can be recorded by utilizing an optical difference based ona reversible structural change at the atomic level. Moreover,information can be reproduced as a difference of the reflected luminousenergy or the transmitted luminous energy at a certain wavelength.Moreover, in this case, it is preferable that the difference betweenluminous energy that is reflected from the first recording areas andluminous energy that is reflected from the second recording areas is atleast 10%. With this configuration, a reproduction signal of the firstrecording area, which corresponds to the write-once information, can beobtained reliably. Moreover, in this case, it is preferable that adifference between an average refractive index of the first recordingareas and an average refractive index of the second recording areas isat least 5%. With this configuration, the difference between theluminous energy reflected from the first recording areas and theluminous energy reflected from the second recording areas can beadjusted to at least 10%. Moreover, in this case, it is preferable thatthe second recording areas of the recording layer are in a crystallinephase. With this configuration, recording can be performed withexcessive laser power. Furthermore, since the luminous energy reflectedfrom the crystalline phase can be large, detection of the reproductionsignal becomes easy. Moreover, in this case, it is preferable that therecording layer comprises a Ge—Sb—Te alloy.

[0024] In a third configuration of an optical disk in accordance withthe present invention, main information and write-once information isrecorded, the write-once information being different for each disk, andthe write-once information storing at least watermark productionparameters for producing a watermark. In accordance with this thirdconfiguration, the following operations can be performed: When thewatermark production parameters and the disk ID are recorded in thewrite-once information with absolutely no correlation between the diskID and the watermark production parameters, it becomes impossible toguess the watermark from the disk ID. Thus, an illegal copier issuing anew ID and issuing an improper watermark can be prevented.

[0025] It is preferable that in the optical disk according to the thirdconfiguration, the main information is recorded by providingconvex-concave pits in a reflective layer, and the write-onceinformation is recorded by partially removing the reflective layer.

[0026] It is preferable that in the optical disk according to the thirdconfiguration, the main information and the write-once information arerecorded by partially changing a reflection coefficient of a reflectivelayer.

[0027] It is preferable that in the optical disk according to the thirdconfiguration, a recording layer comprises a magnetic layer with amagnetic anisotropy in a direction perpendicular to a surface of themagnetic layer, the main information is recorded by partially changing amagnetization direction of the recording layer, and the write-onceinformation is recorded by partially changing the magnetic anisotropy inthe direction perpendicular to the surface of the magnetic layer.

[0028] A first method for recording write-once information onto anoptical disk (a) comprising a disk substrate, and a recording layer onthe disk substrate, including a magnetic film with a magnetic anisotropyin a direction perpendicular to a surface of the magnetic film; and (b)storing write-once information formed by first recording areas andsecond recording areas in a pre-determined portion of the recordinglayer; comprises forming the second recording areas as a plurality ofstripe-shaped marks that are oblong in a radial direction of the disk ina circumferential direction of the disk by irradiating laser light basedon a modulation signal of the write-once information in acircumferential disk direction in the predetermined portion of therecording layer in a manner that a magnetic anisotropy in a directionperpendicular to a surface of the second recording areas becomes smallerthan a magnetic anisotropy in a direction perpendicular to a surface ofthe first recording areas. In accordance with this first method forrecording write-once information onto an optical disk, write-onceinformation that can be used for copyright protection, for example forcopy-protection or protection from unauthorized use of software, can beefficiently recorded onto an optical disk.

[0029] It is preferable that in the first method for recordingwrite-once information, when the second recording areas are formed, alaser light source is pulsed in accordance with a modulation signal ofphase-encoded write-once information, and the optical disk or the laserlight is rotated. With this configuration, rotation variations can beeliminated, especially when the clock of a rotation sensor is used, sothat the write-once information can be recorded with little fluctuationsof the channel clock period.

[0030] It is preferable that in the first method for recordingwrite-once information, the optical disk further comprises a reflectivelayer and a protective layer on the disk substrate, and an intensity oflaser light irradiated to form the second recording areas is smallerthan an intensity of laser light destroying at least one of the disksubstrate, the reflective layer and the protective layer. With thisconfiguration, write-once information can be recorded at softwarecompanies or retailers.

[0031] It is preferable that in the first method for recordingwrite-once information, an intensity of laser light irradiated to formthe second recording areas is an intensity for crystallizing at least aportion of the recording layer. With this configuration, the magneticanisotropy of the recording layer perpendicular to the surface of therecording layer cannot be restored, so that manipulation of thewrite-once information can be prevented.

[0032] It is preferable that in the first method for recordingwrite-once information, an intensity of laser light irradiated to formthe second recording areas is larger than an intensity of laser lightheating the recording layer to a Curie temperature. With thisconfiguration, it is possible to decrease or eliminate the magneticanisotropy of the recording layer perpendicular to the surface of therecording layer, especially when the intensity of the laser light isexcessive.

[0033] It is preferable that in the first method for recordingwrite-once information, an intensity of laser light irradiated to formthe second recording areas is an intensity for making a magneticanisotropy of the magnetic layer of the first recording areas in anin-plane direction dominant.

[0034] It is also preferable that in the first method for recordingwrite-once information, rectangularly stripe-shaped laser light isirradiated with a unidirectional convergence focusing lens onto therecording layer when the second recording areas are formed.

[0035] It is also preferable that in the first method for recordingwrite-once information, a light source of the laser light that isirradiated for forming the second recording areas is a YAG laser. Inthis case, it is preferable that a magnetic field above a certain valueis applied to the recording layer while irradiating laser light from theYAG laser. With this configuration, write-once information can berecorded easily by partially changing the magnetic anisotropyperpendicular to the surface of the recording layer after aligning themagnetic anisotropy in a direction perpendicular to the surface of therecording layer. In this case, it is even more preferable that themagnetic field applied to the recording layer is at least 5 kOe.

[0036] A second method for recording write-once information onto anoptical disk (a) comprising a disk substrate; and on the disk substratea recording layer comprising a film that can be reversibly changedbetween two optically detectable states; and (b) storing write-onceinformation formed by first recording areas and second recording areasin a pre-determined portion of the recording layer; comprises formingthe second recording areas as a plurality of stripe-shaped marks thatare oblong in a radial direction of the disk in a circumferentialdirection of the disk by irradiating laser light based on a modulationsignal of the write-once information in a circumferential disk directionin the pre-determined portion of the recording layer in a manner that aluminous energy of light reflected from the first recording areasdiffers from a luminous energy of light reflected from the secondrecording areas. In accordance with this second method for recordingwrite-once information onto an optical disk, write-once information thatcan be used for copyright protection, for example for copy-protection orprotection from unauthorized use of software, can be efficientlyrecorded onto an optical disk.

[0037] It is preferable that in the second method for recordingwrite-once information, when the second recording areas are formed, alaser light source is pulsed in accordance with a modulation signal ofphase-encoded write-once information, and the optical disk or the laserlight is rotated.

[0038] It is also preferable that in the second method for recordingwrite-once information, the optical disk further comprises a reflectivelayer and a protective layer on the disk substrate, and an intensity oflaser light irradiated to form the second recording areas is smallerthan an intensity of laser light destroying at least one of the disksubstrate, the reflective layer and the protective layer.

[0039] It is also preferable that in the second method for recordingwrite-once information, an intensity of laser light irradiated to formthe second recording areas is an intensity for crystallizing at least aportion of the recording layer.

[0040] It is also preferable that in the second method for recordingwrite-once information, rectangularly stripe-shaped laser light isirradiated onto the recording layer with a unidirectional convergencefocusing lens when the second recording areas are formed. In this case,it is also preferable that a light source of the laser light that isirradiated for forming the second recording areas is a YAG laser.

[0041] A third method for recording write-once information onto anoptical disk comprises producing a watermark based on a disk ID; andoverlapping the watermark on specific data to record it as write-onceinformation. In accordance with this third method for recordingwrite-once information onto an optical disk, the disk ID can be detectedfrom the watermark, so that the origin of illegal copies can bedetermined.

[0042] A first method for reproducing write-once information from anoptical disk (a) comprising a disk substrate, and a recording layer onthe disk substrate, the recording layer including a magnetic film with amagnetic anisotropy in a direction perpendicular to a surface of themagnetic film; and (b) storing write-once information formed by firstrecording areas and second recording areas in a pre-determined portionof the recording layer, the first and second recording layers havingdifferent magnetic anisotropies in a direction perpendicular to asurface of the magnetic layer; comprises irradiating linearly polarizedlaser light onto the pre-determined portion; and detecting a change in apolarization orientation of light reflected from the optical disk orlight transmitted through the optical disk. In accordance with thisfirst method for reproducing write-once information from an opticaldisk, the write-once information can be reproduced easily.

[0043] It is preferable that in the first method for reproducingwrite-once information, the linearly polarized laser light is irradiatedonto the predetermined portion after magnetizing the recording layer ofthe predetermined portion in one step by applying a magnetic field thatis larger than a coercive force of the recording layer in thepre-determined portion. With this configuration, the polarizationorientation detected from the first recording areas is normallyconstant, and the reproduction signal can be obtained with a stableamplitude from the difference with respect to the polarizationorientation of the second recording areas.

[0044] It is also preferable that in the first method for reproducingwrite-once information, the linearly polarized laser light is irradiatedonto the pre-determined portion after aligning a magnetization of therecording layer of the pre-determined portion by applying aunidirectional magnetic field to the pre-determined portion whileincreasing the temperature of the recording layer in the pre-determinedportion above the Curie temperature by irradiating laser light ofconstant luminous energy. With this configuration, after recording thewrite-once information, the signal can be reliably reproduced withoutbeing influenced by outside magnetic fields or the like.

[0045] A second method for reproducing write-once information from anoptical disk (a) comprising a disk substrate; and a recording layer onthe disk substrate, the recording layer including a film that can bereversibly changed between two optically detectable states; and (b)storing write-once information formed by first recording areas andsecond recording areas with different reflection coefficients in apre-determined portion of the recording layer; comprises irradiatingfocused laser light onto the pre-determined portion; and detecting achange in a luminous energy reflected from the disk. In accordance withthis second method for reproducing write-once information from anoptical disk, the write-once information can be reproduced easily.

[0046] A first configuration of an apparatus for reproducing opticaldisks comprising (a) a main information recording area for recordingmain information; and (b) an auxiliary signal recording area overlappingpartly with the main information recording area for recording aphase-encoding modulated auxiliary signal that overlaps a signal of maininformation, comprises means for reproducing a main information signalin the main information recording area with an optical head; firstdecoding means for decoding a main information signal to obtain maininformation data; means for reproducing a mixed signal comprising a maininformation signal in the auxiliary signal recording area and theauxiliary signal as a reproduction signal with the optical head;frequency separation means for suppressing the main information signalin the reproduction signal to obtain the auxiliary signal; and seconddecoding means for phase-encoding decoding the auxiliary signal toobtain the auxiliary data. In accordance with this first configurationof an apparatus for reproducing optical disks, the decoding data of theauxiliary signal can be reproduced reliably.

[0047] It is preferable that in the apparatus for reproducing opticaldisks according to the first configuration, the frequency separationmeans is a low-frequency component separation means for suppressing highfrequency components in the reproduction signal reproduced with theoptical head to obtain a low frequency reproduction signal, and that theapparatus further comprises a second-slice-level setting portion forproducing a second slice level from the low-frequency reproductionsignal; and a second-level slicer for slicing the low-frequencyreproduction signal at the second slice level to obtain a binarizedsignal; wherein the apparatus phase-encoding decodes the binarizedsignal to obtain the auxiliary data. With this configuration, errors dueto variations of the envelope of the reproduction signal of thewrite-once information can be prevented. In this case, it is preferablethat the second-slice-level setting portion comprises auxiliarylow-frequency component separation means with a time constant that islarger than that of the low-frequency component separation means; areproduction signal reproduced with the optical head or a low-frequencyreproduction signal obtained with the low-frequency component separationmeans is entered into the auxiliary low-frequency component separationmeans; and components with frequencies lower than the low-frequencyreproduction signal are extracted to obtain a second slice level. Withthis configuration, the slice level can be set following the levelvariations of low frequency components, so that the signal easily can bereproduced.

[0048] It is preferable that the apparatus for reproducing optical disksaccording to the first configuration further comprises frequencytransformation means for transforming a main information signal includedin a reproduction signal reproduced with the optical head from a timedomain into a frequency domain to produce a first transformation signal;means for producing a mixed signal, wherein auxiliary information hasbeen added or superposed to the first transformation signal; andfrequency inverse-transformation means for transforming the mixed signalfrom the frequency domain to the time domain to produce a secondtransformation signal. With this configuration, the ID signal can bespectrally dispersed, so a deterioration of the video signal, whichcorresponds to the main information, can be prevented, and thereproduction of the main information becomes easier.

[0049] In a second configuration of an apparatus for reproducing opticaldisks, an optical head irradiates linearly polarized light onto anoptical disk, and a change of a polarization orientation of light thatis transmitted or reflected from the optical disk is detected inaccordance with a recording signal on the optical disk. The apparatuscomprises means for moving, when necessary, the optical head into apre-determined portion of the optical disk where write-once informationis stored, and means for reproducing the write-once information afterdetecting a change of a polarization orientation of light that istransmitted or reflected from the pre-determined portion. In accordancewith this second configuration of an apparatus for reproducing opticaldisks, the reproduction signal can be detected easily, because it is notinfluenced by variations of the reflected luminous energy or by noisecomponents included in the addition signal.

[0050] It is preferable that the apparatus for reproducing optical disksaccording to the second configuration further comprises means fordetecting an identifier indicating whether write-once information withincontrol data of the optical disk is present, the indication being basedon a detection signal of detection light that is received with at leastone photo-detector of the optical head or on an addition signal ofdetection signals of detection light that is received with a pluralityof photo-detectors of the optical head, wherein to detect the identifierand to verify whether write-once information is present, the opticalhead is moved to the pre-determined portion of the optical disk wherewrite-once information is stored, when necessary. With thisconfiguration, stripes and defects in the write-once information easilycan be discriminated, so that the start-up time for the apparatus can beconsiderably shortened.

[0051] It is preferable that the apparatus for reproducing optical disksaccording to the second configuration further comprises decoding meansfor phase-encoding decoding during reproduction of the write-onceinformation. This configuration can be used for the reproduction ofwrite-once information, such as an ID signal.

[0052] In a third configuration of an apparatus for reproducing opticaldisks whereon main information is stored and write-once information thatdiffers for each disk is stored, the apparatus comprises a signalreproduction portion for reproducing the main information; a write-onceinformation reproduction portion for reproducing the write-onceinformation; and a watermark attaching portion for producing a watermarksignal based on the write-once information, adding the watermark signalto the main information and giving it out. In accordance with this thirdconfiguration of an apparatus for reproducing optical disks, illegalcopies being made to obtain the main information of, for example, thevideo signal can be prevented.

[0053] It is preferable that in the apparatus for reproducing opticaldisks according to the third configuration, the write-once informationis recorded by partially changing a reflection coefficient of arecording layer on the optical disk.

[0054] It is also preferable that in the apparatus for reproducingoptical disks according to the third configuration, a recording layer ofthe optical disk comprises a magnetic film having a magnetic anisotropythat is perpendicular to a film surface; and write-once information isstored by partially changing the perpendicular magnetic anisotropy ofthe magnetic film.

[0055] It is also preferable that in the apparatus for reproducingoptical disks according to the third configuration, a watermarkattaching portion overlaps a signal of the main information withauxiliary information comprising a watermark. With this configuration,the auxiliary information being deleted from the main information with anormal recording and reproducing system can be prevented.

[0056] It is also preferable that the apparatus for reproducing opticaldisks according to the third configuration further comprises a frequencytransformation means for producing a first transformation signal bytransforming a signal of main information from a time domain into afrequency domain; means for producing a mixed signal by adding orsuperposing write-once information and the first transformation signal;and frequency inverse-transformation means for producing a secondtransformation signal by transforming the mixed signal from thefrequency domain into the time domain.

[0057] It is also preferable that the apparatus for reproducing opticaldisks according to the third configuration further comprises an MPEGdecoder for expanding main information into a video signal; and meansfor inputting the video signal into the watermark attaching portion.With this configuration, the watermark can be spectrally dispersed andadded to the main information, such as the video signal, withoutdeteriorating the signal. In this case, it is preferable that theapparatus further comprises a watermark reproduction portion forreproducing watermarks; the MPEG decoder and the watermark reproductionportion both comprise a mutual authentication portion; and encryptedmain information is sent and decrypted only if the mutual authenticationportions authenticate each other. With this configuration, illegalelimination or manipulation of watermarks can be prevented, because theencryption is not cancelled when the digital signal is intercepted froman intermediate bus. In this case, it is preferable that a compoundsignal of main information that is compounded with an encryption decoderis input into the MPEG decoder. With this configuration, there is nocorrelation between information such as the ID and the watermarkproduction parameters, so that illegal copies with unauthorizedwatermarks can be prevented. In this case, it is even more preferablethat the apparatus further comprises a watermark reproduction portionfor reproducing watermarks; an encryption decoder and the watermarkreproduction portion both comprise a mutual authentication portion; andencrypted main information is sent and decrypted only if the mutualauthentication portions authenticate each other.

[0058] In a first configuration of an apparatus for recording andreproducing optical disks whereon information can be recorded, erasedand reproduced and whereon main information is stored on a mainrecording area of a recording layer of the optical disks using arecording circuit and an optical head, the apparatus comprises means forreproducing write-once information that is recorded onto apre-determined portion of the recording layer using a signal outputportion of the optical head, which detects the write-once information asa change of a polarization orientation; means for recording the maininformation onto the main recording area as encrypted information thatis encrypted with an encryption encoder using the write-onceinformation; and means for reproducing the main information byreproducing the write-once information with the signal output portion ofthe optical head and composing the encrypted information as a decryptionkey in an encryption decoder. In accordance with this firstconfiguration of an apparatus for recording and reproducing opticaldisks, illegal copies can be prevented, so that the copyright can beprotected.

[0059] In a second configuration of an apparatus for recording andreproducing optical disks whereon main information is recorded onto amain recording area of a recording layer of the optical disks using arecording circuit and an optical head, the apparatus comprises awatermark attaching portion for adding a watermark to the maininformation. Write-once information that is stored in a predeterminedportion of the recording layer is reproduced with the optical head. Thereproduced write-once information is added to the main information as awatermark with the watermark attaching portion. The main informationincluding the watermark is recorded onto the main recording area. Inaccordance with this second configuration of an apparatus for recordingand reproducing optical disks, the recording history can be traced fromthe watermark recording data, so that illegal copies and illegal use canbe prevented.

[0060] It is preferable that in the apparatus for recording andreproducing optical disks according to the second configuration, themain information is recorded by partially changing a reflectioncoefficient of the recording layer.

[0061] It is also preferable that in the apparatus for recording andreproducing optical disks according to the second configuration, therecording layer comprises a magnetic film having a magnetic anisotropythat is perpendicular to a film surface; and main information is storedby partially changing a magnetization direction of the magnetic film. Inthis case, it is preferable that the main information and the write-onceinformation are reproduced by detecting a change of a magnetizationorientation of the recording layer or a change of the perpendicularanisotropy of the recording layer with an optical head as a change of apolarization orientation.

[0062] It is also preferable that in the apparatus for recording andreproducing optical disks according to the second configuration, awatermark attaching portion overlaps a signal of the main informationwith auxiliary information comprising a watermark.

[0063] It is also preferable that the apparatus for recording andreproducing optical disks according to the second configuration furthercomprises a frequency transformation means for producing a firsttransformation signal by transforming a signal of main information froma time domain into a frequency domain; means for producing a mixedsignal by adding or superposing write-once information and the firsttransformation signal; and frequency inverse-transformation means forproducing a second transformation signal by transforming the mixedsignal from the frequency domain into the time domain.

[0064] It is also preferable that the apparatus for recording andreproducing optical disks according to the second configuration furthercomprises an MPEG decoder for expanding main information into a videosignal; and means for inputting the video signal into the watermarkattaching portion. In this case, it is preferable that the apparatusfurther comprises a watermark reproduction portion for reproducingwatermarks; the MPEG decoder and the watermark reproduction portion bothcomprise a mutual authentication portion; and encrypted main informationis sent and decrypted only if the mutual authentication portionsauthenticate each other. It is also preferable that a compound signal ofmain information that is compounded with an encryption decoder is inputinto the MPEG decoder. It is even more preferable that the apparatusfurther comprises a watermark reproduction portion for reproducingwatermarks; the encryption decoder and the watermark reproductionportion both comprise a mutual authentication portion; and encryptedmain information is sent and decrypted only if the mutual authenticationportions authenticate each other.

[0065] In a configuration of an apparatus for recording write-onceinformation onto an optical disk storing main information, the apparatuscomprises means for recording auxiliary information comprising at leastone of a disk ID and watermark production parameters. In accordance withthis configuration of an apparatus for recording write-once informationonto an optical disk, it can be determined from the disk ID or thewatermark who made an illegal copy or illegal use of the disk, so thatthe copyright can be protected.

[0066] It is preferable that in the apparatus for recording write-onceinformation onto an optical disk according to this configuration, themain information is stored by providing convex/concave pits in areflection film of the optical disk, and the auxiliary information isstored by partially erasing the reflection film.

[0067] It is also preferable that in the apparatus for recordingwrite-once information onto an optical disk according to thisconfiguration, the main information is stored by partially changing areflection coefficient of a recording layer of the optical disk, and theauxiliary information is stored by partially changing a reflectioncoefficient of the recording layer of the optical disk.

[0068] It is also preferable that in the apparatus for recordingwrite-once information onto an optical disk according to thisconfiguration, a recording layer of the optical disk comprises amagnetic film having a magnetic anisotropy that is perpendicular to afilm surface; main information is stored by partially changing amagnetization direction of the magnetic film; and auxiliary informationis stored by partially changing the perpendicular magnetic anisotropy ofthe magnetic film.

[0069] In a configuration of an apparatus for recording optical disksstoring main information, the apparatus comprises means for producing awatermark based on auxiliary information comprising a disk ID; and meansfor recording data, which consists of certain data to which thewatermark has been superposed. In accordance with this configuration ofan apparatus for recording optical disks storing main information, thewatermark can be detected from the recorded data, and the contentshistory can be determined, so that the copyright can be protected.

BRIEF DESCRIPTION OF THE DRAWINGS

[0070]FIG. 1 is a cross-sectional drawing showing a configuration of anoptical disk in accordance with an embodiment of the present invention.

[0071]FIG. 2 is a cross-sectional drawing showing a configuration of anoptical disk in accordance with another embodiment of the presentinvention.

[0072]FIG. 3 is a drawing illustrating the principle of howmagneto-optical disks are reproduced in accordance with an embodiment ofthe present invention.

[0073]FIG. 4 is a graph showing the Kerr hysteresis loop in aperpendicular direction to the film surface for a BCA portion that hasbeen heated and for a non-BCA portion that has not been heated in therecording layer of the magneto-optical disk in accordance with anembodiment of the present invention.

[0074]FIG. 5 is a graph showing the relation between the laser recordingcurrent for recording identifying information on a magneto-optical diskin accordance with the present invention and the BCA recordingcharacteristics.

[0075]FIG. 6(a) is a traced graph showing a differential signal waveformof a BCA signal at a recording current of 8 A for a magneto-optical diskin accordance with an embodiment of the present invention. FIG. 6(b) isa traced graph showing its addition signal waveform.

[0076]FIG. 7 is a drawing of the optical structure of an apparatus forrecording and reproducing magneto-optical disks in accordance with anembodiment of the present invention.

[0077]FIG. 8 is a process drawing illustrating a method formanufacturing a magneto-optical disk in accordance with an embodiment ofthe present invention.

[0078]FIG. 9 is a process drawing illustrating a method for recordingidentifying write-once information onto a magneto-optical disk inaccordance with an embodiment of the present invention.

[0079]FIG. 10 is a drawing showing a apparatus for detecting BCAidentifying write-once information from a magneto-optical disk inaccordance with an embodiment of the present invention.

[0080]FIG. 11(a) is a schematic drawing illustrating the state of theBCA portions when identifying write-once information that has beenrecorded with excessive power onto a magneto-optical disk in accordancewith an embodiment of the present invention.

[0081]FIG. 11(b) is a schematic drawing illustrating the state of theBCA portions when identifying write-once information that has beenrecorded with adequate power onto a magneto-optical disk in accordancewith an embodiment of the present invention.

[0082]FIG. 12(a) is a schematic drawing showing the result of anobservation with an optical microscope and a polarization microscope ofa BCA portion when BCA identifying write-once information that has beenrecorded with excessive recording power onto a magneto-optical disk inaccordance with an embodiment of the present invention.

[0083]FIG. 12(b) is a schematic drawing showing the result of anobservation with an optical microscope and a polarization microscope ofa BCA portion when BCA identifying write-once information that has beenrecorded with adequate recording power onto a magneto-optical disk inaccordance with an embodiment of the present invention.

[0084]FIG. 13(a) is a graph showing the rotation angle of thepolarization plane in the non-BCA portions of a magneto-optical disk inaccordance with an embodiment of the present invention.

[0085]FIG. 13(b) is a graph showing the rotation angle of thepolarization plane in the BCA portions of a magneto-optical disk inaccordance with an embodiment of the present invention.

[0086]FIG. 14 is a block diagram of an apparatus for reproducing aDVD-ROM and an apparatus for recording and reproducing a DVD inaccordance with an embodiment of the present invention.

[0087]FIG. 15 is a block diagram of a stripe recording apparatus inaccordance with an embodiment of the present invention.

[0088]FIG. 16 is a diagram illustrating the signal waveform and thetrimming for an RZ recording in accordance with an embodiment of thepresent invention.

[0089]FIG. 17 is a diagram illustrating the signal waveform and thetrimming for a PE-RZ recording in accordance with an embodiment of thepresent invention.

[0090]FIG. 18(a) is a perspective drawing of the focusing portion in anembodiment of the present invention.

[0091]FIG. 18(b) is a drawing showing the stripe arrangement and theemitted pulse signal in an embodiment of the present invention.

[0092]FIG. 19 is a diagram showing the stripe arrangement on amagneto-optical disk in accordance with an embodiment of the presentinvention, and the contents of the TOC data.

[0093]FIG. 20 is a flowchart illustrating the switching between CAV andCLV for the stripe reproduction in an embodiment of the presentinvention.

[0094]FIG. 21(a) is a diagram illustrating the data structure after ECCencoding in accordance with an embodiment of the present invention.

[0095]FIG. 21(b) is a diagram illustrating the data structure for n=1after ECC encoding.

[0096]FIG. 21(c) is a diagram illustrating the ECC error correctioncapability in an embodiment of the present invention.

[0097]FIG. 22(a) is a diagram illustrating the data structure of thesynchronized signal.

[0098]FIG. 22(b) is a diagram illustrating the waveform of the fixedpattern.

[0099]FIG. 22(c) is a diagram showing the recording capacities.

[0100]FIG. 23(a) shows the structure of a low-pass filter.

[0101]FIG. 23(b) is a graph showing the waveform of a signal afterpassing through the low-pass filter.

[0102]FIG. 24(a) shows the waveform of the reproduction signal in anembodiment of the present invention.

[0103]FIG. 24(b) explains the dimensional accuracy of the stripes in anembodiment of the present invention.

[0104]FIG. 25 is a flowchart showing how the TOC data is read andreproduced in an embodiment of the present invention.

[0105]FIG. 26 is a block diagram of the second level slice portion in anembodiment of the present invention.

[0106]FIG. 27 shows the waveform of the reproduction signal at differentelements for binarizing the signal in an embodiment of the presentinvention.

[0107]FIG. 28 is a block diagram showing a particular circuit structurefor the second level slice portion in an embodiment of the presentinvention.

[0108]FIG. 29 is a block diagram showing a circuit structure for thesecond level slice portion in an embodiment of the present invention.

[0109]FIG. 30 is a block diagram showing a circuit structure for thesecond level slice portion in an embodiment of the present invention.

[0110]FIG. 31 is a diagram of the actual signal waveform of thereproduction signal at different elements for binarizing the signal inan embodiment of the present invention.

[0111]FIG. 32 is a block diagram showing a disk manufacturing apparatusfor a contents provider and a reproduction apparatus for a systemoperator in accordance with an embodiment of the present invention.

[0112]FIG. 33 is a block diagram showing a disk manufacturing portion ina disk manufacturing apparatus in accordance with an embodiment of thepresent invention.

[0113]FIG. 34 is a block diagram of an entire broadcasting apparatus anda reproduction apparatus on the system operator side in accordance withan embodiment of the present invention.

[0114]FIG. 35 shows graphs of the waveform in the time-domain and thespectrum in the frequency-domain of an original signal and a videosignal in accordance with an embodiment of the present invention.

[0115]FIG. 36 is a block diagram of a receiver on the user side and abroadcasting apparatus on the system operator side in accordance with anembodiment of the present invention.

[0116]FIG. 37 is a block diagram of a watermark detection apparatus inaccordance with an embodiment of the present invention.

[0117]FIG. 38 is a cross-sectional drawing showing the trimming with apulsed laser in accordance with an embodiment of the present invention.

[0118]FIG. 39 is a diagram showing the signal reproduction waveform ofthe trimmed portions in accordance with an embodiment of the presentinvention.

[0119]FIG. 40 is a cross-sectional drawing showing the configuration ofan optical disk in accordance with an embodiment of the presentinvention.

[0120]FIG. 41 is a block diagram showing an apparatus for recording andreproducing optical disks in accordance with an embodiment of thepresent invention.

[0121]FIG. 42 is a block diagram showing an apparatus for recording andreproducing magneto-optical disks in accordance with an embodiment ofthe present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0122] The following is a more detailed description of the presentinvention, with reference to the preferred embodiments.

[0123] First Embodiment

[0124] First of all, the structure of a magneto-optical disk isexplained.

[0125]FIG. 1 is a cross-section showing the structure of amagneto-optical disk in a first embodiment of the present invention. Asis shown in FIG. 1, a dielectric layer 212 is formed on top of a disksubstrate 211, and a recording layer 213 is formed on top of thedielectric layer 212. In the recording layer 213, a plurality of BCAportions 220 a and 220 b (BCA is one of the formats for write-onceidentification information) is recorded in a circumferential directionof the disk. On top of the recording layer 213, an intermediatedielectric layer 214 and a reflecting layer 215 are deposited in thatorder. An overcoat layer 216 is formed on top of the reflecting layer215.

[0126] Referring to FIG. 8, the following is an explanation of a methodfor producing a magneto-optical disk in accordance with this embodiment.

[0127] First of all, as shown in FIG. 8(1), a disk substrate 211, whichhas guide grooves or pre-pits for tracking guidance, is produced byinjection molding using a polycarbonate resin. Then, as is shown in FIG.8(2), an 80 nm thick dielectric layer 212 of SiN is formed on the disksubstrate 211 by reactive sputtering with a Si target in an atmospherecontaining argon gas and nitrogen gas. Then, as is shown in FIG. 8(3), a30 nm thick recording layer 213 consisting of a TbFeCo film is formed onthe dielectric layer 212 by DC sputtering with a TbFeCo alloy target inan argon gas atmosphere. Then, as is shown in FIG. 8(4), a 20 nmintermediate dielectric layer 214 consisting of a SiN film is formed onthe recording layer 213 by reactive sputtering with a Si target in anatmosphere containing argon gas and nitrogen gas. Then, as is shown inFIG. 8(5), a 40 nm thick reflecting layer 215 consisting of an AlTi filmis formed on the intermediate dielectric layer 214 by DC sputtering withan AlTi target in an argon gas atmosphere. Finally, as is shown in FIG.8(6), a 10 μm thick overcoat layer 216 is formed on the reflecting layer215 by dropping an UV-light curing resin on the reflecting layer 215,coating the disk with the UV-light curing resin using a spin-coater at2500 rpm, and curing the UV-light curing resin by irradiating it with UVlight.

[0128] The following is an explanation of a method for recordingidentifying information (write-once information, which is recorded afterfinishing the disk manufacturing process), with reference to FIG. 9.

[0129] First of all, as is shown in FIG. 9(7), the magnetizationorientation of the magnetic layer 213 is aligned into one direction witha magnetizer 217. The recording layer 213 of the magneto-optical disk ofthis embodiment is a vertical magnetization film having a coercive forceof 11 kOe. Thus, the magnetization orientation of the recording layer213 can be aligned with the direction of the magnetic field generated bythe magnetizer 217 by setting the strength of the electric fieldgenerated by the electromagnet of the magnetizer 217 to 15 kGauss, andpassing the magneto-optical disk through this magnetic field. Next, asis shown in FIG. 9(8), using a high-power laser 218, for example a YAGlaser, and a unidirectional convergence focusing lens 219 such as acylindrical lens, the laser light is focused on the recording layer 213in the form of oblong stripes. BCA portions 220 a and 220 b are recordedas identifying information in the circumferential direction of the disk.The recording principle, recording method and reproduction method areexplained in more detail in the course of this specification. Then, asis shown in FIG. 9(9), a BCA reader 221 is used to detect the BCAportions 220 a and 220 b, a PE (phase encode) decoding and a comparisonwith the recorded data is performed to verify whether there is a match.If the BCA portions match the recorded data, the recording of theidentifying information is completed, and if the BCA portions do notmatch, the magneto-optical disk is removed from the process.

[0130] The following is an explanation of the operation principle of theBCA reader 221, with reference to FIG. 10.

[0131] As is shown in FIGS. 10(a) and (c), the BCA reader 221 comprisesa polarizer 222 and a detector 223, whose polarizing planes areperpendicular to each other. Consequently, as is shown in FIGS. 10(a)and (b), when the laser beam is irradiated at the BCA portion 220 a ofthe recording layer 213, no detection signal is output, because thevertical magnetic anisotropy of the BCA portion 220 a is low (themagnetic anisotropy in the in-plane direction is dominant). However,when the laser beam is irradiated at a portion outside the BCA portions(non-BCA portion 224) of the recording layer 213, the polarizing planeof the reflected light rotates and a signal is output to thephoto-detector (PD) 256, because this portion is magnetized in adirection perpendicular to the film surface. Thus, a BCA regenerationsignal as shown in FIG. 10(b) can be attained, and the BCA portions 220can be detected speedily without using an optical head formagneto-optical recording and reproduction.

[0132] Since the magnetic anisotropy in the vertical direction of thefilm surface of the BCA portions is considerably lower, a BCAreproduction signal can be attained for the BCA portions 220 a. Thefollowing is a more detailed explanation of this:

[0133]FIG. 4 shows the hysteresis loop 225 a of a BCA portion 220 of therecording layer 213 that has been heated by irradiation with identifyinginformation, that is, with laser light, and a Kerr hysteresis loop 225 bof a non-BCA portion 224, which has not been heated, in a directionperpendicular to the film plane. It can be seen from FIG. 4, that theKerr rotation angle and the vertical magnetic anisotropy of the heatedBCA portion 220 have been deteriorated considerably. Thus,magneto-optical recording cannot be performed in the heated BCA portions220, because the residual magnetism in the vertical directiondisappears.

[0134] As is shown in FIG. 9, in this embodiment, after themagnetization orientation of the vertical magnetization film in therecording layer 213 has been aligned in one direction (that is, aftermagnetization), the BCA portions 220 are recorded as the identifyinginformation. After the BCA portions 220 have been recorded by layeringthe layers and deteriorating the recording layer 213, the magnetizationorientation of the vertical magnetization film in the recording layer213 can be aligned into one direction while applying a magnetic fieldthat is smaller than the field that has to be applied at roomtemperature by irradiating the recording layer 213 with, for example, astroboscopic light to raise its temperature.

[0135] The recording layer 213 of the magneto-optical disk in thepresent embodiment has a coercive force of 11 kOe at room temperature.However, when it is irradiated by, for example, a stroboscopic light ora laser beam and its temperature is raised to at least 100° C., thecoercive force becomes about 4 kOe, so that when a magnetic field of atleast 5 kOe is applied, the magnetization orientation of the recordinglayer 213 can be aligned into one direction.

[0136] The following is an explanation of the recording power for amagneto-optical BCA recording.

[0137]FIG. 5 shows the BCA recording characteristics for a BCA signalthat was recorded on a magneto-optical disk using a BCA trimming device(BCA recording device—CWQ pulse recording with a YAG laser excited witha 50 W lamp; product by Matsushita Electric Industrial Co., Ltd). As canbe seen from FIG. 5, when the recording current of the laser is below 8A, no BCA portion is recorded. When the recording current of the laseris in the optimal range of 8-9 A, a BCA image 226 a can be attained onlywith a polarization microscope, as is shown in FIGS. 5 and 12(b). ThisBCA image 226 a cannot be observed with an optical microscope. When therecording current of the laser is at least 9 A, the BCA images 226 b and226 c can be attained with both the optical microscope and thepolarization microscope, as is shown in FIGS. 5 and 12(a). When therecording current of the laser as shown in FIG. 5 is higher than 10 A,then the protective layer (overcoat layer) is destroyed. This situationis illustrated in FIG. 11. In FIG. 11, the reflecting layer 215 and theovercoat layer 216 have been destroyed by excessive laser power. On theother hand, when the recording current of the laser is in the optimalrange of 8-9 A, only the recording layer 213 is deteriorated as shown inFIG. 11(b), and the reflecting layer 215 and the overcoat layer 216 areleft intact.

[0138] The following explains a recording/reproduction apparatus formagneto-optical disks according to this embodiment, with reference toFIG. 7.

[0139]FIG. 7 illustrates the optical configuration of arecording/reproduction apparatus for magneto-optical disks according tothe first embodiment of the present invention. FIG. 7 illustrates anoptical head 255 for magneto-optical disks, a pulse generator 254, alaser light source 241, a collimator lens 242, a polarization beamsplitter 243, an objective lens 244 for focusing the laser beam on themagneto-optical disk, a half mirror 246 for separating the lightreflected from the magneto-optical disk into a signal reproductiondirection and a focus tracking control direction, a λ/4-plate 247 forrotating the polarization plane of the light reflected from themagneto-optical disk, a polarization beam splitter 248 for separatingthe light reflected from the magneto-optical disk according to itspolarization plane, photodetectors 249 and 250, and areceiver/controller 253 for focus tracking. Further indicated are amagneto-optical disk according to the present embodiment, a magnetichead 251, and a magnetic head modulation driving circuit 252.

[0140] As is shown in FIG. 7, a linearly polarized laser beam emittedfrom the laser light source 241 is collimated by the collimator lens 242into a parallel laser beam. Only the P-polarized component of thisparallel laser beam passes the polarization beam splitter 243, isfocused by the objective lens 244 and irradiated onto the recordinglayer of the magneto-optical disk 240. Thus, the information concerningthe regular recording data (data information) is recorded by partiallychanging the magnetization orientation of the vertical magnetizationfilm (pointing upwards and downwards). Owing to the magneto-opticaleffect, the orientation of the polarization plane of the light that isreflected (or transmitted) by the magneto-optical disk 240 changesaccording to the magnetization. The reflected light, whose polarizationplane was thus rotated, is irradiated on the polarization beam splitter243, and then separated by the half mirror 246 into a signalreproduction direction and a focus tracking control direction. Thepolarization plane of the beam of the signal reproduction direction isrotated 45° by a λ/4 plate. Then, the P-polarized component and theS-polarized component are separated by the polarization beam splitter248. The light is thus separated into two light beams, whose luminousenergy is detected by the photodetectors 249 and 250. A change in theorientation of the polarization plane is detected as a differentialsignal of the luminous energies detected by the two photodetectors 249and 250. The reproduction signal for the data information is obtainedfrom this differential signal. The focus tracking controller 253 usesthe light that has been separated by the half mirror 246 into the focustracking control direction to control the focus of the objective lens244 and to control tracking.

[0141] The BCA portions 220, serving as identifying information for themagneto-optical disk in his embodiment, are detected with the samereproduction method as the data information. As is shown in FIG. 4, thevertical magnetic anisotropy of the heated BCA portions 220 deterioratesconsiderably (hysteresis loop 225 a). When the recording layer isproduced or when the signal is reproduced, the magnetization directionof the vertical magnetization layer is aligned in one direction, so thatthe polarization plane of a laser beam that is irradiated on the notheated non-BCA portions 224 with greater vertical magnetic anisotropy isrotated for an angle θ_(k) in accordance with the magnetizationdirection. On the other hand, the Kerr rotation angle of the BCAportions 220, which have been heated and whose vertical magneticanisotropy is considerably deteriorated, has become very small, so thatthe polarization plane of a laser beam that is irradiated on the BCAportions 220 hardly rotates at all when reflecting the laser beam.

[0142] The following is a method for aligning the magnetizationdirection of the vertical magnetization film into one direction, whenthe BCA portions are reproduced: A magneto-optical diskrecording/reproduction apparatus as shown in FIG. 7 irradiates a laserbeam of at least 4 mW onto the magnetic layer 213 of a magneto-opticaldisk 240, so that the magnetic layer 213 is heated to at least the Curietemperature. At the same time, the magnetic head 251 applies a constantmagnetic field of at least 200 Oe, so that the magnetization directionof the recording layer of the BCA portions is aligned into onedirection.

[0143]FIG. 6(a) shows an actual traced waveform of the detecteddifferential signal for the identifying data. FIG. 6(b) shows a tracedwaveform of the detected all-sum signal of the identifying signal, whichis a summation signal detected with several photo-detectors. As can beseen from FIG. 6(a), the identifying information can be detected as apulse waveform with a sufficient amplitude ratio in the differentialsignal. Even when the magnetic properties of the recording layer changeor a portion of the recording layer is crystallized, the change of theaverage refractive index will be less than 5%, so that the variations inthe luminous energy of the light reflected from the magneto-optical diskare less than 10%. Consequently, the variations of the reproductionwaveform caused by a change of the luminous energy of the reflectedlight are very small.

[0144]FIG. 13 illustrates the polarization of the reflected lightcompared to that of the incident light. As is shown in FIG. 13(b), lightreflecting from the heated BCA portions 220 has exactly the samepolarization direction 227 b as incident light. On the other hand, lightreflecting from the non-BCA portions 224 has a polarization direction227 a that, owing to the Kerr effect in the magnetization film havingwith vertical magnetization anisotropy, is rotated by a rotation angleθ_(k) against the polarization direction of the incident light.

[0145] Moreover, this embodiment detects the identifying informationfrom a differential signal. Using this reproduction method, variationsof the luminous energy that do not follow the polarized light can bealmost completely canceled, so that the noise due to these luminousenergy variations can be reduced.

[0146] Second Embodiment

[0147]FIG. 2 is a cross-section showing the structure of amagneto-optical disk in a second embodiment of the present invention. Asis shown in FIG. 2, a dielectric layer 232 is formed on top of a disksubstrate 231, and a tri-layer recording layer comprising a magneticreproduction film 233, an intermediate magnetic film 234, and a magneticrecording film 235 is formed on top of the dielectric layer 232. In therecording layer, a plurality of BCA portions 220 a and 220 b is recordedin a circumferential direction of the disk. On top of the recordinglayer, an intermediate dielectric layer 236 and a reflecting layer 237are deposited in that order. An overcoat layer 238 is formed on top ofthe reflecting layer 237.

[0148] Referring to FIG. 8 of the first embodiment and to FIG. 9, thefollowing is an explanation of a method for producing a magneto-opticaldisk in accordance with this embodiment.

[0149] First of all, a disk substrate 231, which has guide grooves orpre-pits for tracking guidance, is produced by injection molding using apolycarbonate resin. Then, an 80 nm thick dielectric layer 232 of SiN isformed on the disk substrate 231 by reactive sputtering with a Si targetin an atmosphere containing argon gas and nitrogen gas. The recordinglayer comprises a magnetic reproduction film 233 of GdFeCo with a Curietemperature of T_(c1) and a coercive force of H_(c1), an intermediatemagnetic film 234 of TbFe with a Curie temperature of T_(c2) and acoercive force of H_(c2), and a magnetic recording film 235 of TbFeCowith a Curie temperature of T_(c3) and a coercive force of H_(c3). Thesefilms are formed on top of the dielectric layer 232 by DC sputteringwith alloy targets in an Ar gas atmosphere. Then, a 20 nm intermediatedielectric layer 236 consisting of a SiN film is formed on the recordinglayer by reactive sputtering with a Si target in an atmospherecontaining argon gas and nitrogen gas. Then, a 40 nm thick reflectinglayer 237 consisting of an AlTi film is formed on the intermediatedielectric layer 236 by DC sputtering with an AlTi target in an argongas atmosphere. Finally, an 8 μm thick overcoat layer 238 is formed onthe reflecting layer 237 by dropping an UV-light curing resin on thereflecting layer 237, coating the disk with the UV-light curing resinusing a spin-coater at 300 rpm, and curing the UV-light curing resin byirradiating it with UV light.

[0150] The reproduction magnetic layer 233 is set to a thickness of 40nm, a Curie temperature T_(c1) of 300° C., and a coercive force H_(c1)of 100 Oe at room temperature. The intermediate magnetic film 234 is setto a thickness of 10 nm, a Curie temperature T_(c2) of 120° C., and acoercive force H_(c2) of 3 kOe at room temperature. The magneticrecording film 235 is set to a thickness of 50 nm, a Curie temperatureT_(c3) of 230° C., and a coercive force H_(c3 of) 15 kOe at roomtemperature.

[0151] The following explains the reproduction principle for thetri-layer recording layer of this embodiment with reference to FIG. 3.FIG. 3 shows a reproduction magnetic field 228, laser light spots 229 a,229 b, and 229 c, recording domains 230, a magnetic reproduction film233, an intermediate magnetic film 234, and a magnetic recording film235. As is shown in FIG. 3, the domains 230 containing the informationsignals are recorded into the magnetic recording film 235. At roomtemperature, the magnetization of the magnetic recording film 235 istransferred to the magnetic reproduction film by coupling forces betweenthe magnetic recording film 235, the intermediate magnetic film 234, andthe magnetic reproduction film 233. At signal reproduction, theregeneration magnetic film 233 retains the signal of the magneticrecording film 235 in the low temperature portion 229 b of the laserbeam spot 229 a. In the high temperature portion 229 c of the laser beamspot 229 a, however, the temperature of the intermediate magnetic film234 rises above the Curie temperature, so that the coupling forcesbetween the recording magnetic layer 235 and the reproduction magneticlayer 233 are interrupted and the magnetization direction of themagnetic reproduction film 233 is aligned with the magnetizationdirection of the magnetic reproduction film 228, because the Curietemperature of the intermediate magnetic film 234 is lower than that ofthe other magnetic films. Therefore, the recording domains 230 becomemasked by the high temperature portion 229 c, which is a part of thelaser beam spot 229 a. Consequently, the signal can be reproduced onlyfrom the low temperature portion 229 b of the laser beam spot 229 a.This reproduction method is a magnetically induced super resolutionmethod called “FAD”. Using this reproduction method, a signalreproduction with regions smaller than the laser beam spot becomespossible.

[0152] A similar reproduction is also possible when the magneticallyinduced super resolution method called “RAD” is used, wherein signalreproduction is possible only in the high temperature portion of thelaser beam spot.

[0153] The following explains the recording method for identifyinginformation (write-once information) in a magneto-optical disk of thisembodiment,-with reference to FIG. 9.

[0154] First of all, as is shown in FIG. 9(7), the magnetizationorientation of the recording layer is aligned into one direction withthe magnetizer 217. The magnetic recording film 235 of the recordinglayer in the magneto-optical disk of this embodiment is a verticalmagnetization film having a coercive force of 15 kOe. Thus, themagnetization orientation of the recording layer can be aligned with thedirection of the magnetic field generated by the magnetizer 217 bysetting the strength of the electric field generated by theelectromagnet of the magnetizer 217 to 20 kGauss, and passing themagneto-optical disk through this magnetic field. Next, as is shown inFIG. 9(8), using a high-power laser 218, for example a YAG laser, and aunidirectional convergence focusing lens 219 such as a cylindrical lens,the laser light, is focused on the recording layer in form of oblongstripes. BCA portions 220 a and 220 b are recorded in thecircumferential direction of the disk. The recording principle,recording method and reproduction method are the same as in the firstembodiment. As in the first embodiment, the recording layer also can bemagnetized after the BCA recording. When the temperature of therecording layer is raised for magnetization using, for example, astroboscopic light, the magnetization orientation of the recording layeralso can be aligned into one direction with a magnetic field that is assmall as 5 kOe.

[0155] The recording layer of this embodiment is a tri-layer andcomprises the magnetic reproduction film 233, the intermediate magneticfilm 234, and the magnetic recording film 235, The identifyinginformation can be recorded by considerably decreasing the magneticanisotropy in a direction perpendicular to the film surface in at leastthe portion where the magnetic recording film 235 has been heated, andletting the magnetic anisotropy in substantially in-plane directionsdominate.

[0156] The Curie temperature and the coercive force of the magnetic filmconstituting the recording layer can be changed relatively easily bychoosing a material with different structure or by adding atoms withdifferent vertical magnetic anisotropy. Therefore, the conditions forproducing the recording layer of the magneto-optical disk and theconditions for recording the identifying information can be optimallyset.

[0157] In the first and second embodiments, a polycarbonate resin isused for the disk substrates 211 and 231, a SiN film is used for thedielectric layers 212, 214, 232, and 236, and a TbFeCo film, a GdFeCofilm, and a TbFe film are used for the magnetic films. However, it isalso possible to use glass or plastic, such as a polyolefin or PMMA, forthe disk substrates 211 and 231. It is also possible to use othernitride films such as AlN, or oxide films such as TaO₂, or chalcogencomposition films such as ZnS, or a film of a mixture of at least two ofthe above for the dielectric layers 212, 214, 232, and 236. It is alsopossible to use rare earth metal—transition metal ferrimagnetic film ofa different material or structure, or a MnBi film, PtCo film or anyother magnetic film with vertical magnetic anisotropy for the magneticfilm.

[0158] Moreover, In the second embodiment, the vertical magneticanisotropy of the magnetic recording film 235 in the tri-layer recordinglayer was deteriorated. However, the same effect can be attained whenthe vertical magnetic anisotropy of either the magnetic reproductionfilm 233 or the magnetic recording film, or both, or the verticalmagnetic anisotropy of the magnetic reproduction film 233, theintermediate magnetic film 234, and the magnetic recording film 235 isdeteriorated.

[0159] Third Embodiment

[0160]FIG. 40 is a cross-section showing the structure of amagneto-optical disk in a third embodiment of the present invention. Asis shown in FIG. 40, a dielectric layer 302 is formed on top of a disksubstrate 301, and a recording layer 303 of a phase-changeable materialthat can reversibly change between a crystal phase and an amorphousphase is formed on top of the dielectric layer 302. In the recordinglayer 303, a plurality of BCA portions 310 is recorded in acircumferential direction of the disk. On top of the recording layer303, an intermediate dielectric layer 304 and a reflecting layer 305 aredeposited in that order. An overcoat layer 306 is formed on top of thereflecting layer 305. Two optical disks, of which only the first diskhas the overcoat layer 306 are laminated by adhesion layer 307. It isalso possible to laminate together two optical disks of the sameconfiguration by hot-melting.

[0161] The following is an explanation of a method for producing amagneto-optical disk in accordance with this embodiment.

[0162] First of all, a disk substrate 301, which has guide grooves orpre-pits for tracking guidance, is produced by injection molding using apolycarbonate resin. Then, an 80 nm thick dielectric layer 302 ofZnSSiO₂ is formed on the disk substrate 301 by high-frequency RFsputtering with a ZnSSiO₂ target in an atmosphere containing argon gas.Then, a 20 nm recording layer 303 of a GeSbTe alloy is formed on top ofthe dielectric layer 302 by RF sputtering with a GeSbTe alloy in an Argas atmosphere. Then, a 60 nm intermediate dielectric layer 304consisting of a ZnSSiO₂ film is formed on the recording layer 303 by RFsputtering with a ZnSSiO₂ target in an atmosphere containing argon gas.Then, a 40 nm thick reflecting layer 305 consisting of an AlCr film isformed on the intermediate dielectric layer 304 by DC sputtering with anAlCr target in an argon gas atmosphere. Then, a 5 μm thick overcoatlayer 306 is formed on the reflecting layer 305 by dropping an UV-lightcuring resin on the reflecting layer 305, coating the disk with theUV-light curing resin using a spin-coater at 3000 rpm, and curing theUV-light curing resin by irradiating it with UV light. Thus, a firstoptical disk is obtained. Similarly, a second optical disk is obtained,but without forming the overcoat layer. Finally, the first and thesecond optical disks are laminated to each other by hot-melting, andcuring an adhesive that forms an adhesive layer 307.

[0163] The recording of information on the recording layer 303 of theGeSbTe alloy uses local changes in the portions where laser light isfocused on a microscopic spot. In other words, the difference of theoptical properties between the crystal phase and the amorphous phase,which are based on reversible structural changes on the atomic level,are used. The recorded information can be reproduced by detecting thedifference of the reflected luminous energy or the transmitted luminousenergy at a certain wavelength.

[0164] When an optical disk has a recording layer consisting of a thinfilm that can be reversibly changed between these two opticallydetectable states, it can be used as a high-density rewritableexchangeable medium, for example a DVD-RAM.

[0165] The recording method for identifying information (write-onceinformation) according to this embodiment can be almost the same as inthe first and the second embodiment. That is, using a high-power laser,for example a YAG laser, and a unidirectional convergence focusing lenssuch as a cylindrical lens, a laser beam is focused on the recordinglayer 303 as oblong stripes. BCA portions 310 are recorded in thecircumferential direction of the disk. When a laser beam with higherpower than for the recording of information in the recording layer 303is irradiated on the optical disk of this embodiment, an excessivestructural change due to crystallization by phase transition occurs.Thus, it becomes possible to non-reversibly record the BCA portions 310.It is preferable that the BCA portions 310 are recorded asnon-reversible crystal phases. By thusly recording the BCA portions 310(i.e. the identifying information) the luminous energy reflected fromthe portions where identifying information is recorded differs from theluminous energy reflected from other portions. Therefore, as in thefirst embodiment, the identifying information can be reproduced with anoptical head. It is preferable that the difference of the luminousenergies reflected from the optical disk is at least 10%. By setting thedifference of the average refractive indices to at least 5%, the changeof the reflected luminous energies can be set to at least 10%. In thecase of DVD-RAMs, as in the case of DVD-ROMs, not only an excessivestructural change of the recording layer can be brought about, but it isalso possible to raise the difference of the reflected luminous energiesabove a certain value by partially destroying the protective layer orthe reflecting layer to reproduce the BCA signal. Moreover, since it isa laminated structure, there are no problems with reliability.

[0166] The following explains an apparatus and a method for recordingidentifying information (write-once information) in accordance with thepresent invention with reference to the drawings.

[0167] Since the identifying information is compatible with diskrecording/reproduction apparatuses for DVDs, the technology forrecording identifying information on a DVD and the format of therecorded signal is explained in more detail, whereas explanations on thereproduction signal pattern of the magneto-optical disk are omitted.However, since the identifying information in a high-densitymagneto-optical disk such as an ASMO (Advanced Stage Magneto-OpticalDisk) is performed with an optical head 255 as shown in FIG. 7, and thereproduction conditions are different from the detection method of therecording signal.

[0168]FIG. 15 is a block diagram of a laser recording apparatusaccording to an embodiment of the present invention. FIG. 16 illustratesthe signal waveform and trimming shape of an “RZ recording” in anembodiment of the present invention. As is shown in FIG. 16(1), thepresent invention uses an RZ recording for the identifying information.In an RZ recording, one time unit is divided into several timeslots, forexample a first timeslot 920 a, a second timeslot 921 a, a thirdtimeslot 922 a, etc. When the data is “00”, a pulse 924 a whose width isnarrower than the timeslot period (that is, the period T of the channelclock) in the first timeslot 920 a (that is, between t=t1 and t=t2), asshown in FIG. 16(1). Influences of rotational instabilities of the motor915 shown in FIG. 15 can be removed by letting a clock signal generator913 generate the clock signal in accordance with a rotational pulse froma rotation sensor 915 a of the motor 915, and synchronizing therecording therewith. The stripe 923 a in the first recording area 925 aof the four recording areas on the disk, which indicates a “00”, istrimmed with the laser, as is shown in 16(2).

[0169] When the data is “01”, a pulse 924 b whose width is narrower thanthe timeslot period (that is, the period T of the channel clock) isrecorded in the second timeslot 921 b (that is, between t=t2 and t=t3),as shown in FIG. 16(3). The stripe 923 b in the second recording area926 b of the four recording areas on the disk, which indicates a “01”,is trimmed by the laser, as is shown in 16(4).

[0170] A “10” and a “11” are recorded in the third timeslot 922 a andthe fourth timeslot, respectively.

[0171] Thus, a circumferential barcode as shown in FIG. 39(1) isrecorded on the disk.

[0172] The following explains the “NRZ recording” used in a conventionalbarcode recording. In a NRZ recording, a pulse with the same width asthe timeslot period (that is, the period T of the channel clock) isrecorded. In the RZ recording of the present invention, (1/n) T issufficient for the pulse width of one pulse, but for a NRZ recording, abroader width T is necessary for the pulse width. When several T'sfollow upon each other, a double or triple pulse width of 2T or 3Tbecomes necessary.

[0173] With laser trimming as in the present invention, it is necessaryto change the configuration of the apparatus itself to change the linewidth for laser trimming, which is difficult to realize and notpractical for NRZ recording. Consequently, to represent a “00”, stripesof the temporal width T are formed in the first and third recording areataken from the left, and to represent a “10”, a stripe of the temporalwidth 2T is formed in the second and third recording area taken from theleft.

[0174] In conventional NRZ recording, the pulse width is 1T or 2T, sothat it is clear that the laser trimming of the present invention is notapplicable. The stripes (barcode) recorded by the laser trimming of thepresent invention are reproduced as shown in FIG. 6(a) or FIG. 31(1),which show experimental results. However, the trimming line width variesfrom disk to disk, so that a precise control is very difficult. Thereason for this is that when the reflecting film or the recording layerof the optical disk is trimmed, the trimming line width varies owing tovariations of the pulse laser output power, thickness and material ofthe reflecting layer, and thermal conductivity and thickness of the disksubstrate. Moreover, when barcodes with different line widths areprovided on the same disk, the structure of the recording apparatusbecomes complicated. For example, for an NRZ recording used for aproduct barcode, the trimming line width has to be matched precisely tothe channel clock period, that is 1T, 2T, 3T or, generally speaking, nT.It is particularly difficult to change the line widths between 2T, 3Tetc. while recording the bars. The barcode format for conventionalproducts is NRZ, so that when it is applied to the laser barcode of thepresent invention, it is difficult to precisely record different linewidths of 2T, 3T etc. on the same disk, which decreases the yield.Moreover, since the laser trimming line width varies, a stable recordingcannot be achieved and decoding becomes difficult. By using RZ recordingas in the present invention, a stable digital recording can be achieved,even when the laser trimming line width varies. Moreover, there has tobe only one laser trimming line width for RZ recording, so that it isnot necessary to modulate the laser power and the structure of therecording apparatus can be simple.

[0175] Thus, by combining several RZ recordings, a laser barcode for anoptical disk of the present invention can achieve a stable digitalrecording.

[0176] The following explains the PE modulation of an RZ recording. FIG.17 shows the signal waveform and trimming form of the PE-modulated RZrecording in FIG. 16. First of all, if the data is “0”, a pulse 924 awith a temporal width that is smaller than the time slot period (that isthe channel clock period T) is recorded in the left timeslot 920 a (thatis between t=t1 and t=t2) of the two timeslots 920 a and 921 a, as shownin FIG. 17(1). If the data is “1”, a pulse 924 b with a temporal widththat is smaller than the time slot period (that is the channel clockperiod T) is recorded in the right timeslot 921 b (that is between t=t2and t=t3) of the two timeslots 920 b and 921 b, as shown in FIG. 17(3).A stripe 923 a indicating a “0” is recorded in the left recording area925 a, and a stripe 923 b indicating a “1” is recorded in the rightrecording area 926 b by laser trimming, as shown in FIGS. 17(2) and (4).Thus, in the case of a “010”, a pulse 924 c is recorded in the lefttimeslot (to represent “0”), a pulse 924 d is recorded in the righttimeslot (to represent “1”), and a pulse 924 e is recorded in the lefttimeslot (to represent “0”), as shown in FIG. 17(5). The stripes aretrimmed by a laser in the left, the right and again the left recordingareas of two recording areas each on the disk. FIG. 17(5) shows thesignal for the PE-modulated data “010”. As is shown in FIG. 17(5), thereis a signal for each channel bit. In other words, the signal density isusually constant and DC-free. Since this PE modulation is DC-free, it isrobust against low-frequency components, even when the pulse edge isdetected at reproduction time. Consequently, the decoding circuit forthe disk reproduction apparatus can be simpler. Moreover, since there isat least one pulse 924 within a channel clock time of 2T, a clock thatis synchronized with the channel clock can be reproduced without using aPLL.

[0177] In this manner, a circular barcode as shown in FIG. 39(1) isrecorded on the disk. To record the data “01000” of FIG. 39(4) with thePE-RZ recording of this embodiment, a barcode 923 corresponding to therecording signal 924 of FIG. 39(3) is recorded as shown in FIG. 39(2).When the optical pickup of the reproduction apparatus reproduces thisbarcode, a reproduction signal with a waveform as shown in FIG. 39(5) isattained, because the reflection signal in a portion of the pitmodulation signal is lost due to defective portions in the reflectinglayer of the barcode. After passing the regeneration signal through asecond-order or third-order Tchebychev LPF 943 as shown in FIG. 23(a), asignal with the waveform shown in FIG. 39(6) is attained. This signal issliced with a level slice portion, and the reproduction data “01000”shown in FIG. 39(7) is reconstructed.

[0178] As is explained with FIGS. 11(a) and (b), when laser trimmingwith excessive power is performed on a single-substrate magneto-opticaldisk, the overcoat layer (protective layer) is destroyed. Consequently,after laser trimming was performed with excessive power, it is necessaryto reform the protective layer at the factory. Therefore, barcoderecording cannot be performed at software companies or retailers, sothat its application will be very limited. It is also possible thatthere will be problems with its reliability.

[0179] Laser trimming recordings of write-once information onsingle-substrate magneto-optical disks without destroying the overcoatlayer (protective layer) can be achieved by heating only the recordinglayer and changing the magnetic anisotropy in the directionperpendicular to the film surface. When this was experimentallyverified, there was no change in the magnetic properties after 96 hoursat 85° C. and 95% humidity.

[0180] On the other hand, when the laser trimming recording method ofthe present invention was applied to a laminated disk of two opticaldisks with transparent substrates, the protective layer remains withoutbeing destroyed, which was experimentally verified with a ×800 opticalmicroscope. Also in a similar experiment with a magneto-optical disklasting 96 hours at 85° C. and 95% humidity, no change in the reflectionfilm at the trimmed portions could be observed. Thus, by applying thelaser trimming recording method of the present invention to laminateddisks, such as DVDs, the protective layer does not have to be reformedat the factory, so that a barcode laser trimming recording can beperformed at places other than the press factory, for example, atsoftware companies or at retailers. Therefore, it is not necessaryanymore to give secret keys of software company codes to anyone outsidethe company, so when security information, such as a serial number forcopy protection, is recorded in the barcode, its security can be greatlyimproved. As will be explained further below, by setting the trimmingline width for DVDs to 14T (that is, 1.82 μm), the barcode can beseparated from the pit signals of the DVD, so that the barcode can berecorded superimposed on the pit recording areas of the DVD. Thus, byapplying the trimming method and the modulation recording method of thepresent invention to a laminated disk, such as a DVD, a secondaryrecording can be performed after shipping from the factory. A secondaryrecording also can be performed by applying the same recording method tomagneto-optical disks.

[0181] The following explains the operation of the laser recordingapparatus with reference to FIG. 15. As is shown in FIG. 15, first, theentered data is merged with an ID number issued by a serial numbergenerator 908 in an input portion 909. An encryption encoder 830 signsor encrypts with an encryption function such as RSA or DES, asnecessary. An ECC encoder 907 performs error correction encoding andadds interleaf. Then, a PE-RZ modulation is performed with a PE-RZmodulator 910. A clock signal generator 913 generates the modulationclock by synchronizing the rotation pulse from a motor 915 or a rotationsensor 915 a. Based on the PE-RZ modulation signal, a laser emissioncircuit 911 generates a trigger pulse. This trigger pulse is input intoa high-power laser 912, for example a YAG laser, driven by a laser powercircuit 929. Thereby, pulsed laser light is emitted, which is focused bya focusing member 914 on the recording layer 235 of a single-substratemagneto-optical disk 240, or on the recording layer 303 of a laminateddisk 300, or on the reflecting film 802 of a laminated disk 800. Thisproduces a barcode-shaped deterioration recording or erasure of therecording layers 235, 303 or the reflecting film 802. Error correctiontechniques will be explained in more detail further below. The adoptedencryption method is to sign the private key of the software companyused by the public key code as the serial number. Doing so, nobody butthe software company has the private key, and since it is not possibleto come up with a new serial number, the unlawful issuance of serialnumbers by parties other than the software company can be prevented.Also, since the public key cannot be read “backwards” the security ofthe system is high. Thus, even when the public key is recorded on thedisk and transmitted with the reproduction apparatus, counterfeiting canbe prevented. The magneto-optical disk 240, the DVD-RAM disk 300 and theDVD-ROM disk 800 are discriminated by the disk discriminator 260, whichuses the reflection coefficient and a means for reading the disk-typeidentifying information. In the case of a magneto-optical disk 240, therecording power is lowered and the lens is defocused. Thus, a stable BCArecording can be recorded on the magneto-optical disk 240.

[0182] The following paragraph explains the focusing member 914 of thelaser recording apparatus with reference to FIG. 18.

[0183] As is shown in FIG. 18(a), the light from the laser 912 enters afocusing member 914, and is collimated by a collimator 912 a. Acylindrical lens 917 focuses the laser light only in the circumferentialdirection on the optical disk, so that the light turns into a stripeextending in the radial direction. A mask 918 trims this light, and afocusing lens 919 focuses the light on the recording layer 235 of themagneto-optical disk 240, or the recording layer 303 of the DVD-RAM disk300, or the reflection film 802 of the DVD-ROM disk 800. The recordinglayers 235, 303 or the reflection film 802 are deterioration-recorded orerased in stripe-form. The mask 918 controls the four sides of thestripe. However, in reality, it is sufficient if only one peripheralside in the longitudinal direction of the stripe is controlled. Thus, astripe 923 as shown in FIG. 18(b) can be recorded on the disk. In PEmodulations, the three stripe intervals 1T, 2T and 3T are possible.Discrepancies from these intervals cause jitter, which brings the errorrate up. Since in the present invention the clock generator 913generates the recording clock in sync with the rotation pulse from themotor 915, and passes it on to the modulator 910, the stripes 923 can berecorded precisely in accordance with the motor 915, or in other words,with the rotation of the magneto-optical disk 240, the DVD-RAM disk 300,or the DVD-ROM disk 800. Therefore, jitter can be reduced. It is alsopossible to scan a continuously excited laser in a radial direction andform a barcode using a scanning means for the laser.

[0184]FIG. 19 illustrates the characteristics of the disk format. As isshown in FIG. 19, on a DVD, all data are recorded with CLV. However, thestripes 923 of the present invention are recorded by CAV, overlappingthe prepit signals of the read-in data areas (overlap-writing), whichare recorded with CLV. Thus, the CLV data are recorded by a pit patternon the master record, whereas the CAV data are recorded by deleting thereflective film off with the laser. Because of this overlap-writing,pits are recorded between 1T, 2T, and 3T of the barcode stripes. Usingthis pit information, tracking with an optical head becomes possible,and T_(max) and T_(min) of the pit signal can be detected. Thus, therotation speed of the motor can be controlled by detecting thesesignals. If the relation between the trimming width t of the stripes andthe pit clock T(pit) is t>14T(pit), T_(min) can be detected, and therotation speed of the motor can be controlled by detecting this signal.If t is shorter than 14T(pit), its pulse width becomes the same, and itis impossible to discern the stripes 923 a and the pits, so thatdecoding becomes impossible. Moreover, since the address information ofthe pits is read at the same radial position as the stripes, the addressinformation can be obtained and track jumping performed, because thelength of the address region 944 contains at least one frame of pitinformation. Moreover, as is shown in FIG. 24, by providing a ratio,i.e. a duty ratio, between stripes and non-stripes of less than 50%,that means T(S)<T(NS), the substantial reflection coefficient only drops6 dB, so that the focus of the optical head can be applied steadily.There are players that cannot control tracking due to the stripes, butsince the stripes 923 are CAV data, reproduction by optical pickup ispossible, if driving is performed using a rotation pulse from, forexample, a Hall element of the motor 17 and CAV rotation.

[0185] In magneto-optical disks, the variation of the reflectioncoefficient is less than 10%, so that it has absolutely no influence onthe focus control.

[0186]FIG. 20 is a flowchart showing the order of operations when thepit data of the optical tracks in the stripe area are not reproducedcorrectly. When the optical disk is inserted (step 930 a), first theoptical head is moved to the inner perimeter of the optical disk (step930 b) and accesses the stripes 923 shown in FIG. 19. When the pitsignals in the area of the stripes 923 are not all correctly reproduced,the rotational phase control for CLV cannot be applied. Therefore,rotation speed control is applied by measuring the frequency or T_(max)or T_(min) of the pit signals with a rotation sensor of the hole elementof the motor (step 930 c). Then, it is determined whether there arestripes or not (step 930 i). If there are no stripes the optical headmoves to the outer perimeter of the optical disk (step 930 f). If thereare stripes, the stripes (barcode) are reproduced (step 930 d). Then, itis determined whether the reproduction of the barcodes is finished (step930 e). If the reproduction of the barcodes is finished, the opticalhead moves to the outer perimeter of the disk (step 930 f). Since thereare no stripes in this area, the pit signals are completely reproducedand the focus and tracking servo are applied correctly. Moreover, sincethe pit signals are completely reproduced in this manner, a regularcontrol of the rotation phase becomes possible (step 930 g) and CLVrotation is possible. Therefore, the pit signal can be correctlyreproduced in step 930 h.

[0187] Thus, by switching between rotation speed control and rotationphase control, two different types of data, namely data of stripes(barcodes) and data recorded in pits, can be reproduced. Because thestripes (barcodes) are at the innermost perimeter of the optical disk,it is possible to switch between the two kinds of rotation control, i.e.rotation speed control and rotation phase control, by measuring theposition of the optical head in the radial direction of the disk usingan optical head stopper and the address information of the pit signals.

[0188] The format for high-speed switch recording is illustrated by thedata structure for synchronized encoded data in FIG. 22.

[0189] The fixed pattern in FIG. 22(a) is “01000110”. Usually, a patternsuch as “01000111” with the same number 0's and 1's is normal for afixed pattern, but in the present invention, the data rather has thisstructure. The reason for this is as follows: To perform high-speedswitch recording, at least two pulses have to fit into it. Since thedata area is a PE-RZ recording as shown in FIG. 21(a), high-speed switchrecording is possible. However, the synchronized coding in FIG. 22(a) isarranged as irregular channel bits, so that in regular methods there maybe two pulses within it, in which case high-speed switch recordingcannot be performed. In the present invention, the fixed pattern is forexample “01000110”. Consequently, as is shown in FIG. 22(b), there isone pulse on the right side of T₁, no pulse in T₂, one pulse on theright side of T₃, and one pulse on the left side of T₄, and there is notimeslot with two pulses. Therefore, by adopting synchronized coding inthe present invention, high-speed switch recording becomes possible, andthe production speed can be doubled.

[0190] The following is an explanation of a recording/reproductionapparatus. FIG. 14 is a block diagram of a recording/reproductionapparatus. The following explanation concentrates on decoding. Alow-pass filter 943 eliminates high-frequency components due to the pitsfrom the stripe signal output. In case of a DVD, the signal of a maximumof 14T with T=0.13 μm may be reproduced. In this case, high-frequencycomponents can be eliminated by passing the signal through asecond-order or third-order Tchebychev low-pass filter 943 as shown inFIG. 23(a), as was experimentally verified. In other words, if alow-pass filter of at least second order is used, the pit signal and thebarcode signal can be differentiated, and the barcode can be reliablyreproduced. FIG. 23(b) shows the waveform for a worst-case simulation.

[0191] Thus by using a low-pass filter 943 of at least second order, thepit regeneration signal can be eliminated almost completely, and thestripe regeneration signal can be output, so that the strip signal canbe reliably decoded.

[0192] Returning to FIG. 14, a PE-RZ decoder 930 a decodes the digitaldata, and this data is error-corrected by an ECC decoder 930 b. Then, adeinterleaving portion 930 d cancels the interleaf, and an RS decoder930 c performs the calculations for decoding the Reed-Solomon coding, toperform error correction. As is shown by the data structure in FIG.21(a), the interleaf and the Reed-Solomon error correction encoding areperformed with an ECC encoder 907, as shown in FIG. 15. Consequently, byadopting this data structure, if the byte error rate before correctionis 10⁻⁴, a disk error will occur in only one out of 10⁷ disks, as isshown in FIG. 21(c). As is shown in FIG. 22(a), in this data structure,one sync code is assigned for every four synchronized encodings toreduce the data length of the code, whereby the sync code can be reducedto ¼ pattern, which increases the efficiency.

[0193] The following explains the scalability of this data structurewith reference to FIG. 22. As is shown in FIG. 22(c), in the presentinvention, the recording capacity can be between, for example, 12 byteand 188 byte, and can be arbitrarily raised by steps of 16 byte. FIG.21(a) shows that n can change between n=1 to n=12. If, for example, n=1,as in FIG. 21(b), there are only four-data rows 951 a, 951 b, 951 c, and951 d, and the following rows are the ECC rows 952 a, 952 b, 952 c, and952 d. The data row 951 d becomes the 4-byte EDC row. Thus, theremaining rows 951 e to 951 z are taken to be filled with 0's, and errorcorrection-coding is performed. This ECC encoding is performed by theECC encoder 907 if the laser recording apparatus in FIG. 15, andrecorded as a barcode on the disk. If n=1, only 12 bytes can be recordedover an angular range of 51°. Similarly, if n=2, 18 bytes are recorded,and if n=12, 271 bytes are recorded over an angular range of 336°.

[0194] In the present invention, this scalability has a purpose.Moreover, the production tact time is important for the laser trimming.If the BCA recording areas are trimmed one by one, a slow apparatus cantake more than 10 seconds to record a maximum of several thousands.Since the production tact time is four seconds, this will slow down theproduction tact time. On the other hand, the main object for applicationof the present invention is first of all the disk ID, for which about 10bytes should suffice. If 271 bytes are written instead of 10 bytes, thelaser processing time will rise six-fold, so that the production costincreases. Employing the scalability method of the present invention canreduce production cost and time.

[0195] The ECC encoder 930 b of the recording/reproduction apparatus inFIG. 14, can error-correct data from 12 bytes to 271 bytes with the sameprogram, by, for example, filling up the rows 951 e to 951 z with 0's ifn=1 as in FIG. 21(b).

[0196] As is shown in FIG. 24, for 1T, the pulse width of 4.4 μs becomesabout one half of the stripe interval of 8.92 μs. For 2T, the pulsewidth is 4.4 μs for a stripe interval of 17.84 μs, and for 3T, the pulsewidth is 4.4 μs for a stripe interval of 26.76 μs, so that, taking theaverage for a PE-RZ modulation, about ⅓ corresponds to the pulse portion(reflection coefficient about zero). Consequently, in a disk with astandard reflection coefficient of 70%, the reflection coefficient dropsto about ⅔, that is, to about 50%, and thus can be reproduced with aregular ROM disk player.

[0197] Moreover, in magneto-optical disks, the average refractive indexof the recording layer does not change, and the average change of thereflection coefficient is less than 10%, so that level fluctuations ofthe reproduction waveform are small and compatibility with DVD playersis easy.

[0198] The following is an explanation of the reproduction order withreference to the flowchart in FIG. 25. When the disk is inserted, first,the TOC (Control Data) is reproduced (step 940 a). In optical disksaccording to the present invention, a stripe existence identifier 937 isrecorded as a pit signal in the TOC of the TOC region 936, as is shownin FIG. 19. Therefore, when the TOC is reproduced, it can be verifiedwhether stripes are recorded or not. Then, it is determined whether thestripe existence identifier 937 is “0” or “1” (step 940 b). If thestripe existence identifier 937 is “0”, the optical head moves towardsthe outer perimeter of the optical disk, switches to rotation phasecontrol and performs a regular CLV reproduction (step 940 f). If thestripe existence identifier 937 is “1”, it is determined whether thestripes are on the opposite side of the reproduction side, that is,whether they are recorded on the reverse side of the disk (thereverse-side stripe existence identifier 948 is “1” or “0”) (step 940h). If the reverse-side stripe existence identifier 948 is “1”, therecording layer on the reverse side of the optical disk is reproduced(940 i). If the reverse side of the optical disk cannot be reproducedautomatically, a reverse-side reproduction instruction is given out anddisplayed. If it is known in step 940 h that stripes are recorded on theside that is being reproduced, the optical head is moved to the regionof the stripes 923 on the inner perimeter of the optical disk (step 940c), the rotation speed control is switched, and the stripes 923 arereproduced with CAV rotation (step 940 d). Then, it is determinedwhether the reproduction of the stripes 923 has finished (step 940 e).If the reproduction of the stripes 923 has finished, the optical headmoves towards the outer perimeter of the optical disk, switches again torotation phase control, and performs regular CLV regeneration (step 940f), to regenerate the data of the pit signals (step 940 g).

[0199] Thus, by recording a stripe existence identifier 937 in the pitregion of the TOC, the stripes 923 can be reliably reproduced. If thestripe existence identifier on the optical disk is not defined, theregion of the stripes 923 cannot be properly tracked, so that time hasto be spent to discriminate between stripes 923 and defects. In otherwords, even when there are no stripes, an attempt is made to read thestripes, and it has to be verified in a separate step, whether there arereally no stripes, or whether they are perhaps located even more towardsthe inner perimeter, so that extra time is needed to start up thereproduction process. Moreover, since the reverse-side stripe existenceidentifier 948 has been recorded, it can be determined whether thestripes 923 are recorded on the reverse side. Therefore, even in thecase of an optical disk such as a double-sided DVD, the barcode stripes923 can be reliably reproduced. In a DVD-ROM, the inventive stripes passthrough both reflecting layers of a double-sided disk, so that they alsocan be read from the reverse side. Reading the reverse-side stripeexistence identifier 948, the stripes 923 can be reproduced from thereverse side by encoding the stripes backwards at recording time. As isshown in FIG. 22(a) the present invention uses “01000110” for thesynchronized coding. Consequently, when reproduced from the reverseside, the synchronized coding “01100010” is detected. Therefore, it canbe detected whether the barcode stripes 923 are reproduced from thereverse side. In that case, a second decoder 930 of therecording/reproduction apparatus of FIG. 14 decodes the code backwards,so that even when a double-sided disk is reproduced from the reverseside, the penetrating barcode stripes 923 can be correctly reproduced.Moreover, as is shown in FIG. 19, a write-once stripe data existenceidentifier 939 and the stripe recording capacity are recorded in theTOC. Consequently, when stripes 923 have already been recorded in afirst trimming, the recordable amount for a second trimming of stripes938 can be calculated. Therefore, when the recording apparatus in FIG.15 performs the second trimming, it can be determined from the TOC datahow much more can be recorded. As a result, it can be prevented that therecording exceeds 360° and the stripes 923 of the first trimming aredestroyed. As is shown in FIG. 19, by leaving an empty portion 949 of atleast one pit signal frame between the stripes 923 of the first trimmingand the stripes 938 of the second trimming, it can be prevented that theprevious trimming data is destroyed.

[0200] Since a trimming counter identifier 947 is recorded in thesynchronized coding portion, as shown in FIG. 22(b), the stripes 923 ofthe first trimming and the stripes 938 of the second trimming can bediscriminated. If there were no trimming counter identifier 947, thefirst stripes 923 and the second stripes 938 could not bedifferentiated.

[0201] The following is an explanation of the procedure from contents todisk production with reference to FIG. 33. As is shown in FIG. 33,first, the original contents 3 of, for example, a motion picture areencoded in blocks with a variable length scheme and turned into acompressed video signal, such as image-compressed MPEG, in a diskmanufacturing portion 19. This signal is scrambled by the encryptionencoder 14 with the encryption key 20 for activation. This scrambledcompressed video signal is recorded as a pit-shaped signal on a masterdisk 6 with the master disk production apparatus 5. Using the masterdisk 6 (or a molding die, or a stamper) and a molding apparatus 7, alarge-volume disk substrate 8 with recorded pits is manufactured and areflecting layer of, for example, aluminum is formed with a reflectinglayer forming apparatus 15. Two disk substrates 8 and 8 a are laminatedwith a laminating apparatus 9 to finish a laminated disk 10. In case ofa magneto-optical disk, the compressed video signal is recorded as amagneto-optical signal in the recording layer. In case of a single-sideddisk, the disk 240 a is finished without laminating. In case of aDVD-RAM disk, the compressed video signal is similarly recorded in therecording layer, and two disk substrates are laminated with a laminatingapparatus 9 to finish laminated disk 300. For DVD-RAMs, there aresingle-sided disks with a recording layer only on one side, anddouble-sided with a recording layer on both sides.

[0202] The following is an explanation of level slicing for the BCA withreference to the FIGS. 38 and 39.

[0203] As shown in FIG. 38(1), in a BCA recording with a laser, a pulsedlaser 808 irradiates laser light on an aluminum reflection film 809 of alaminated disk 800, so that stripe-shaped low-reflection portions 810are recorded as PC modulation signals by trimming the aluminumreflection film 809. Thus, as shown in FIG. 38(2), BCA stripes areformed on the disk. When these BCA stripes are reproduced with a regularoptical head, the reflection signal from the BCA portion disappears, sothat the modulation signal is generated from the signal-lacking portions810 a, 810 b, 810 c, which are intermittently lacking a modulationsignal. A modulation signal with 8-16 modulation of the pits is slicedat a first slice level 915 to decode the main signal. On the other hand,since the signal level of the signal-lacking portion 810 a is low, iteasily can be sliced at the second slice level 916. The barcodes 923 aand 923 b shown in FIG. 39(2) are sliced at the slice level S₂ shown inFIG. 39(5), so that they can be reproduced with a regular opticalpickup. As is shown in FIG. 39(6), a digital signal can be attained byslicing the signal, after suppressing high-frequent pit signalcomponents with a low-pass filter, at the second slice level S₂. ByPE-RZ decoding this digital signal, a digital signal as shown in FIG.39(7) is output. The actual appearance of the reproduction signal isshown in FIG. 31.

[0204] The following is an explanation of the decoding with reference toFIG. 14.

[0205] As is shown in FIG. 14, a disk 800 with a BCA includes twotransparent substrates that are laminated together with the recordinglayer 802 a on the inside. There may be one recording layer 802 a or tworecording layers 802 a and 802 b. When there are two recording layers, astripe existence identifier 937 (see FIG. 19) indicating whether thereis a BCA is recorded in the control data of the first recording layer802 a near the optical head 255. In this case, because the BCA is in thesecond recording layer 802, the focus is on the first recording layer802 a, and the optical head 255 is moved to the radial position of thecontrol data on the innermost perimeter of the second recording region919. Since the control data is main information, it is recorded by EFM,8-15, or 8-16 modulation. Only when the stripe existence identifier 937in the control data is “1”, the one-layer/two-layer switching portion827 changes the focus to the second recording layer 802 b to reproducethe BCA. Using the first level slice portion 590 and slicing at aregular first slice level 915 as shown in FIG. 38(3), the BCA isconverted into a digital signal. This signal is decoded by an EFMdecoder 925, an 8-15 modulator-decoder 926 or an 8-16 modulator-decoder927 in the first decoder 928. Then it is error-corrected by the ECCdecoder 36, and output as main information. The BCA is only read outwhen the control data in this main information is reproduced and thestripe existence identifier is “1”. When the stripe existence identifier937 is “1”, the CPU 923 issues an instruction to the one-layer/two-layerswitching portion 827, and drives the focus adjusting portion 828 toswitch the focus from the first recording layer 802 a to the secondrecording layer 802 b. At the same time, the optical head 255 is movedto the radial position of the second recording region 920 (in the DVDstandard, this is the BCA recorded between 22.3 mm and 23.5 mm from theinner perimeter of the control data), and the BCA is read out. In theBCA region, the envelope of the partially missing signal in FIG. 38(3)is reproduced. By setting the luminous energy for the second slice level916 of the second level-slice portion 929 below the first slice level915, the reflection portions and the missing portions of the BCA can bedetected, and the digital signal output. This signal is decoded in thePE-RZ decoder 930 a of the second decoder 930 and ECC-decoded in the ECCdecoder 930 b to give out the BCA data, which is auxiliary information.Thus, the main information is decoded and reproduced by the firstdecoder 928, and the BCA data, which is auxiliary information, isdecoded and reproduced by the second decoder.

[0206]FIG. 24(a) shows the reproduction waveform before passing thelow-pass filter 943, FIG. 24(b) shows the processing precision of theslits in the low-reflection portion, and FIG. 23(b) shows the simulatedwaveform after passing the low-pass filter 943. It is difficult toprovide slits with a width below 5-15 μm. Moreover, if a recording isperformed further than 23.5 mm from the disk center, the recording datawill be destroyed. For DVDs, the largest capacity after formatting islimited to 188 bytes, due to the limitations of the shortest recordingperiod of 30 μm, and the largest radius of 23.5. mm.

[0207] The following is a detailed specific example for setting thesecond slice level 916 and the operation of the second level sliceportion 929.

[0208]FIG. 26 is a detailed view of the second level slice portion 929.The waveform for this explanation is shown in FIG. 27.

[0209] As is shown in FIG. 26, the second level slice portion 929comprises a light-reference-value setting portion 588 feeding the secondslice level 916 to the second level slicer 587, and a frequency divider587 d for frequency-dividing the output signal of the second levelslicer 587. Moreover, the light-reference-value setting portion 588comprises a low-pass filter 588 a and a level converter 588 b.

[0210] The following explains its operation. In the BCA region, theenvelope of the partially missing signal as shown in FIG. 27(1) isreproduced due to the BCA. In this reproduction signal, high-frequencycomponents due to the signal and low-frequency components due to the BCAsignal are mixed. However, the high-frequency components of the 8-16modulation can be suppressed with the low-pass filter 943, and only thelow-frequency signal 932 of the BCA signal as shown in FIG. 27(2) isentered into the second level slicer 929.

[0211] When the low-frequency signal 932 is entered into the secondlevel slice portion 929, the light-reference-value setting portion 588filters out even lower frequency components (almost DC) of thelow-frequency signal 932 with a low-pass filter 588 a with a timeconstant that is larger than the time constant of the low-pass filter943 (in other words, the low-pass filter 588 a extracts low-frequencycomponents). The level converter 588 b adjusts the signal to a suitablelevel, so that a second slice level 916 as illustrated by the fat linein FIG. 27(2) is output. As is shown in FIG. 27(2), the second slicelevel 916 tracks the envelope.

[0212] In the present invention, when the BCA is read, a rotation phasecontrol cannot be performed, and tracking control is also not possible.Consequently, the envelope incessantly fluctuates as in FIG. 27(1). Ifthe slice level were constant, the fluctuating reproduction signal couldbe mistaken, causing the error rate to go up. Therefore, it would not beappropriate to carry data. However, with the circuit in FIG. 26 of thepresent invention, the second slice level is constantly corrected andfitted to the envelope, so that wrong slicing can be significantlyreduced.

[0213] Thus, the present invention is not affected by a fluctuatingenvelope, and the second level slicer 587 slices the low-frequencysignal 932 at the second slice level 916, before outputting a binarizeddigital signal such as the one shown in FIG. 27(3). At the start of thebinarized digital signal output from the second level slicer 587, thesignal is reversed, and a digital signal as shown in FIG. 27(4) isoutput. Accordingly, FIG. 28 shows the specific circuits for a frequencydividing means 934 and a second level slice portion 929.

[0214] Thus, by setting the second slice level 916, differences in thereflection coefficient of different disks, variations in the luminousenergy due to aging of the reproduction laser, and low-frequency level(DC level) variations of the 8-16 modulation signal due totrack-crossing at reproduction time can be absorbed, and a reproductionapparatus for optical disks can be provided that can reliably slice theBCA signal.

[0215] The following explains another method for slicing the secondslice level 916. FIG. 29 shows another circuit diagram for the frequencydividing means 934 and the second level slice portion 929. As is shownin FIG. 29, the low-pass filter 943 of the frequency dividing means 934comprises a first low-pass filter 943 a with a small time constant and asecond low-pass filter 943 b with a large time constant. The secondlevel slicer 587 of the second level slice portion 929 comprises aninverting amplifier 687 a, a DC reproduction circuit 587 b, a converter587 c, and a frequency half-divider 587 d. The waveform for this exampleis shown in FIG. 31.

[0216] The following explains its operation. In the BCA region, theenvelope of the partially missing signal as shown in FIG. 31(1) isreproduced due to the BCA. This reproduction signal is entered into afirst low-pass filter 943 a and a second low-pass filter 943 b of thelow-pass filter 943. The first low-pass filter 943 a with the smallertime constant eliminates the high-frequency signal components of the8-16 modulation from the reproduction signal, and outputs the BCAsignal. The first low-pass filter 943 b with the larger time constantpasses the DC components of the reproduction signal, and outputs the DCcomponent of the reproduction signal. When the first low-pass filter 943a suppresses the high-frequency components of the 8-16 modulation andenters this signal into the inverting amplifier 587 a, the invertingamplifier 587 a amplifies the amplitude, which has been reduced bypassing through the first low-pass filter 943 a. The amplified signal isDC-reproduced at GND level in the DC reproduction circuit 587 b, and asignal as shown in FIG. 31(3) is entered into the comparator 587 c. Onthe other hand, when the second low-pass filter 943 b enters the DCcomponent of the reproduction signal into the light-reference-valuesetting portion 588, the light-reference-value setting portion 588adjusts the signal with a resistive divider to an appropriate level andenters the second slice level 916 into the comparator 587 c, as shown inFIG. 31(2). The comparator 587 c slices the output signal of the CDreproduction circuit 587 b at the second slice level 916 and outputs abinarized digital signal as shown in FIG. 31(4). At the start of thedigital signal, which has been binarized by the comparator 587 c, thefrequency half-divider 587 d reverses the signal, and a digital signalis output. Accordingly, FIG. 28 shows the specific circuits for afrequency dividing means 934 and a second level slice portion 929.

[0217]FIG. 30 shows a specific circuit of the frequency dividing means934 and the second level slice portion 929 to accomplish this.

[0218] Thus, by setting the second slice level 916 to reproduce the BCAsignal, differences in the reflection coefficient of different disks,variations in the luminous energy due to aging of the reproductionlaser, and low-frequency level (DC level) variations of the 8-16modulation signal due to track-crossing at reproduction time can beabsorbed, and reproduction apparatus for optical disks can be providedthat can slice the BCA signal reliably. Moreover, when the circuits arediscrete, the number of elements can be minimized, and a reliable BCAreproduction circuit can be achieved.

[0219] Moreover, if this signal can be loaded into the CPU and decodedby software, the clock frequency of the PE modulation signal can bereduced to one half with the frequency half-divider 587 d. Therefore,even when a CPU with a slow sample frequency is used, the threshold ofthe signal can be detected reliably.

[0220] This effect also can be attained by slowing down the rotationfrequency of the motor at reproduction time. This will be explained withFIG. 14. When the command has been issued to reproduce the BCA, the CPUsends a rotation speed deceleration signal 923 b to the rotationcontroller 26. Then, the rotation controller 26 decelerates the rotationfrequency of the motor 17 to one half or one quarter. Therefore, thefrequency of the reproduction signal decreases, and can be decoded bysoftware even when a CPU with a slower sample frequency is used, and aBCA with a small linewidth can be reproduced. Sometimes, productionfacilities manufacture BCA stripes with a small linewidth, but byslowing down the rotation frequency they can be handled with slow CPUs.This improves the error rate and the reliability at BCA reproductiontime.

[0221] When the BCA is read at a regular speed (such as single speed),the CPU 923 sends a deceleration command to the rotation controller 26to halve the rotation frequency of the motor 17 only when an erroroccurred in the BCA reproduction. Adopting this method, the actualread-out speed for a BCA with an average linewidth does not decrease atall. Only when the linewidth is narrow and errors occur, the errors canbe correctly detected by reading the BCA at half the speed. Thus, byslowing down the read-out speed for narrow BCA linewidths, a slowdown ofthe BCA reproduction speed can be prevented.

[0222] In FIG. 14, a low-pass filter 943 is used as the frequencydividing means 934 but an envelope-tracking circuit or a peak-hold alsocan be used as long as it is a means for suppressing high-frequencysignals of the 8-16 modulation from the reproduction signal of the BCAregion.

[0223] The frequency dividing means 934 and the second level slicer 929also can be means for directly binarizing the reproduction signal of theBCA region, then entering the reproduction signal into a microprocessor,discriminating the 8-16 signal and the BCA signal on the time axis bydigitally processing using points with difference of edge intervals, andsubstantially suppressing the high-frequency signal of the 8-16modulation.

[0224] The modulation signal is recorded with pits by 8-16 modulation toobtain the high-frequency signal 933 in FIG. 14. On the other hand, theBCA signal becomes the low-frequency signal 932. Thus, since in the DVDstandard, the main information is a high-frequency signal 933 of amaximum of 4.5 MHz, and the auxiliary information is a low-frequencysignal 932 with a period of 8.92 μs, that is, about 100 kHz, theauxiliary information easily can be frequency-divided with the low-passfilter 943. Using a frequency dividing means 934 comprising a low-passfilter 943 as shown in FIG. 14, the two signals easily can be divided.In this case, the low-pass filter 943 can be of a simple configuration.

[0225] The preceding was an outline of the BCA.

[0226]FIG. 32 is a block drawing of a disk manufacturing apparatus and areproduction apparatus. As is shown in FIG. 32, the disk manufacturingportion 19 manufactures laminated ROM or RAM disks or single-substratedisks 10 with the same contents. Using a BCA recorder 13, the diskmanufacturing apparatus 21 PE-modulates BCA data 16 a, 16 b, 16 cincluding the identification codes 12 a, 12 b, 12 c, such as IDs thatare different for each disk, and forms barcode-shaped BCAs 18 a, 18 b,18 c on the disks 10 a, 10 b, 10 c by trimming with a YAG-laser. In thefollowing, the disks whereon a BCA 18 has been recorded are referred toas BCA disk 11 a, 11 b, and 11 c. As is shown in FIG. 32, the pitportion and the recording signal on the BCA disks 11 a, 11 b, and 11 care completely the same. However, a different (for example,incrementally numbered) ID is recorded into the BCA 18 of each disk.Contents providers, such as film studios, can record these IDs into anID data base 22. When the disks are shipped, the BCA data is read with abarcode reader 24 that can read BCA, and it is recorded which disk withwhich ID has been distributed at what time to which system operator 23,that is, CATV studio, broadcasting station or airline.

[0227] A record about which disk ID has been distributed to which systemoperator at what time is recorded in the ID data base 22. Therefore, ifa large number of illegal copies of a certain BCA disk is put intocirculation, it can be traced by checking the real watermark to whichsystem operator the illegally copied disk had been originallydistributed. This feature will be detailed further below. Since this IDnumbering based on the BCA performs virtually the same role as awatermark for the entire system, it is called “prewatermarking”.

[0228] The following is an explanation of the data to be recorded in theBCA. An ID generator 26 generates IDs. Moreover, a watermark-productionparameter generator 27 generates watermark-production parameters basedon these IDs or on random numbers. Then, the ID and thewatermark-production parameters are mixed signed by a digital signatureportion 28 using the private key of a public key cryptography. The BCArecorder 13 records the ID, the watermark-production parameters and thesignature data onto each disk 10 a, 10 b, and 10 c. Thus, the BCAs 18 a,18 b, and 18 c are formed.

[0229] If main information, such as a video signal, is recorded on theBCA disks 11 a, 11 b, or 11 c, the BCA reproduction portion 39 firstreads out the BCA signal including the different IDs, as shown in FIG.41. Then, a watermark recording portion 264 converts the video signal bysuperimposing the BCA signal and a recording circuit 272 records theconverted video signal on the BCA disks 11 a, 11 b, and 11 c (300 (240,800) in FIG. 41). When the video signal onto which the BCA signal hasbeen superimposed is reproduced from the BCA disk 300 (240, 800), theBCA reproduction portion 39 reads out the BCA signal of the disk, anddetects it as the ID1 of the disk. A watermark reproduction portiondetects the video signal onto which the watermark has been superimposedas disk ID2. A comparator compares the ID1 read out from the BCA signalwith the disk ID2 read out from the watermark of the video signal, andwhen the two IDs do not match, the reproduction of the video signal isstopped. As a result, the video signal of an illegal disk onto which awatermark that is different from the BCA signal has been superimposedcannot be replayed. On the other hand, if both IDs match, a descrambler31 descrambles the video signal with the superimposed watermark using acompound key comprising ID information read out from the BCA signal, andthe video signal is output.

[0230] The BCA disks 10 a, 10 b, and 10 c that have been“pre-watermarked” with such a disk manufacturing apparatus 21 are thensent to the system operators 23 a, 23 b, and 23 c with the reproductionapparatuses 25 a, 25 b, and 25 c. In FIG. 32, elements of thebroadcasting apparatus 28 have been partially left out for the sake ofconvenience.

[0231]FIGS. 34 and 35 illustrate the operation performed by the systemoperators. FIG. 34 is a block diagram showing the broadcasting apparatus28 in detail. FIG. 35 is a graph showing the waveform of the originalsignal and the video signals on the time axis and their waveforms on thefrequency axis.

[0232] As is shown in FIG. 34, the broadcasting apparatus 28 set up in aCATV station comprises a reproduction apparatus 25 a for systemoperators, and the disk 11 a with BCA supplied by, for example, the filmstudio, is inserted into this reproduction apparatus 25 a. The maininformation of the signal that is reproduced with the optical head 29 isreproduced with the data reproduction portion 30, descrambled with thedescrambler 31, expanded to the original movie signal with the MPEGdecoder 33, and sent to the watermark portion 34. The original signal asshown in FIG. 35(1) is first entered into the watermark portion 34, andtransformed by, for example, FFT from the time domain into the frequencydomain by a frequency converter 34 a. Thus, the frequency spectrum 35 ashown in FIG. 35(2) is attained. A spectrum mixer 36 mixes the frequencyspectrum 35 a with the ID signal having the spectrum shown in FIG.35(3). As shown in FIG. 35(4), the spectrum 35 b of the mixed signal isthe same as the frequency spectrum 35 a of the original signal shown inFIG. 35(2). In other words, the ID signal is spectrally dispersed. Thissignal is transformed from the frequency domain to the time domain by,for example, inverse FFT with an inverse frequency converter 37, and asignal as in FIG. 35(5), which is almost the same as the original signal(FIG. 35(1)) is obtained. Because the ID signal is spectrally dispersedin the frequency domain, the deterioration of the video signal isnegligible.

[0233] The following explains how the ID signal 38 is produced.

[0234] A digital signature verification portion 40 verifies thesignature of the BCA data reproduced from the BCA disk 11 a by the BCAreproduction portion 39 with, for example, the public key sent from, forexample, an IC card 41. If the signature is invalid, the operation ishalted. If the signature is valid, this shows that the data has not beenmanipulated and the ID is sent unchanged to a watermark-data productionportion 41 a. Using the watermark-production parameters contained in theBCA data, a watermark signal corresponding to the ID signal shown inFIG. 35(3) can be generated. The watermark signal also can be generatedby calculating the watermark from the ID data or the card ID of the ICcard 41.

[0235] In that case, the ID has absolutely nothing to do with thewatermark-production parameters, so that if the watermark-productionparameters and the ID are recorded in the BCA, the watermark can not bededucted from the ID. In other words, only the copyright owner knows therelation between ID and watermark. Therefore, watermarks being illegallyissued to make illegal copies and issue new IDs can be prevented.

[0236] On the other hand, a spectral signal can be generated by acertain calculation from the card ID of the IC card 41 to bury the cardID of the IC card 41 as a watermark in the video output signal by addingit to the ID signal 38. In this case, both the circulated (that is,supplied by sales) ID of the software and the ID of the reproductionapparatus can be verified so that the tracing of illegal copies becomeseasy.

[0237] The video output signal of the watermark portion 34 is sent tothe output portion 42. If the broadcasting apparatus 28 broadcasts acompressed video signal, the video output signal is compressed with anMPEG encoder 43, scrambled with a scrambler 45 using the systemoperator's own encryption key 44 and broadcast from the broadcastingportion 46 to the audience via a network or radio waves. In this case,the compression parameter information, such as the transfer rate afterthe original MPEG signal has been compressed, is sent from the MPEGdecoder 33 to the MPEG encoder 43, so that the compression ratio can beincreased even with real-time encoding. Moreover, the compressed audiosignal 48 can bypass the watermark portion 34 to avoid expansion andcompression, so that a deterioration of the audio quality can beavoided.

[0238] Then, if no compressed signal is broadcast, the video outputsignal 49 is scrambled unchanged and broadcast from the broadcastingportion 46 a to the audience via a network or radio waves. In videosystems on board airplanes, scrambling is unnecessary. Thus, a videosignal with a watermark is broadcast from the disk 11 a with BCA.

[0239] An illegal copier could intercept the signal from an intermediatebus between two components in FIG. 34 to obtain the video signalbypassing the watermark portion 34. To avoid this, the buses between thedescrambler 31 and the MPEG decoder 33 and the watermark portion 34 areencrypted by handshake between the mutual authentication portions 32 aand 32 b, as well as between the mutual authentication portions 32 c and32 d. When an encrypted signal is transmitted by the mutualauthentication portion 32 c on the sender side to the mutualauthentication portion 32 c on the receiver side, the mutualauthentication portion 32 c and the mutual authentication portion 32 dcontact each other, that is, they perform a handshake. Only if theresult of the handshake is correct, does the mutual authenticationportion 32 d on the sender side cancel the encryption. This is the samewith the mutual authentication portion 32 a and the mutualauthentication portion 32 b. Thus, with the method of the presentinvention, the encryption is canceled only in the case of mutualauthentication. Therefore, even when the digital signal is taken from anintermediate bus, the encryption has not been canceled and since thewatermark portion 34 cannot be bypassed in the end, an unlawfulelimination or manipulation of the watermark can be prevented.

[0240] Thus, the receiver 50 on the user side receives the watermarkedvideo signal 49 transmitted with a transmitter 46 of the broadcastingapparatus 28 on the system-operator side, as is shown in FIG. 36. In thereceiver, a second descrambler 51 cancels the scrambling, and if thesignal is compressed, an MPEG decoder 52 expands the signal, which isthen output from an output portion 53 as a video signal 49 a to amonitor 54.

[0241] The following discusses the illegal copying. The video signal 49a can be intercepted and recorded on a tape 56 with a VTR 55, and alarge number of illegal copies of the tape 56 thus can be multiplied andcirculated (by sales), resulting in an infringement of the rights of thecopyright holder. However, if the BCA of the present invention is used,there is a watermark in the video signal 49 a and in the video signal 49b (see FIG. 37) that is reproduced from a video tape 56. Because thewatermark has been added in the frequency domain, it cannot be easilyeliminated. Also, it cannot be eliminated by passing the signal througha regular recording/reproduction system.

[0242] The following is an explanation of how the watermark can bedetected, with reference to FIG. 37.

[0243] An illegally copied recording medium 56, for example a video tapeor a DVD laser disk is reproduced with a reproduction apparatus 55 a,such as a VTR or a DVD player. The reproduced video signal 49 b is fedinto a first input portion of a watermark detection apparatus 57. Afirst spectrum 60, which is a spectrum of the illegally copied signal,as shown in FIG. 35(7) is obtained with a first frequency converter 59 aby, for example, FFG or DCT. The original contents are fed into a secondinput portion 58 a, and a second spectrum 35 a is obtained bytransformation into the frequency domain with a second frequencyconverter 59 a. Such a spectrum is shown in FIG. 35(2). When thedifference between the first spectrum 60 and the second spectrum 35 a istaken with a subtractor 62, a differential spectrum signal 63 as shownin FIG. 35(8) can be obtained. This differential spectrum signal 63 isgiven into an ID detector 64. The ID detector 64 retrieves the watermarkparameters for the n-th ID from an ID database 22 (step 65), inputs them(step 65 a), and compares the spectrum signal based on the watermarkparameters with the differential spectrum signal 63 (step 65 b). Then,it is determined whether the spectrum signal based on the watermarkparameters and the differential spectrum signal 63 match. If the twomatch, this means the ID corresponds to the n-th watermark, so that ID=n(step 65 d). If the two do not match, ID is renewed to n+1, and thewatermark for the (n+1)th watermark is retrieved from the ID database.These steps are repeated to detect the ID of the watermark. If the IDmatches, the spectrums in FIGS. 35(3) and (8) match. The ID of thewatermark is output from an output portion 66, and it can be seen fromwhere the unauthorized copy came.

[0244] Thus, because the ID of the watermark can be determined asdescribed above, the origin of the pirated disks or unauthorized copiescan be traced, so that the copyright can be protected.

[0245] If a system that combines the BCA of the present invention with awatermark records the same video signal on a ROM disk or a RAM disk, andrecords watermark information in the BCA, it can realize a virtualwatermark. The system operator can bury watermarks corresponding to theIDs that are issued to the contents providers in the video signal thatis eventually output from the reproduction apparatus. Compared withconventional methods for recording video signals with watermarks thatdiffer for each disk, the disks' cost and production time can be reducedsignificantly. A watermark circuit is needed in the reproductionapparatus, but since FFT and IFFT are staple techniques, this will notplace an undue burden upon the broadcasting devices.

[0246] In this example, a spectrum-dispersion watermark portion wasused, but the same effect can be obtained with other types of watermarkportions as well.

[0247] For a DVD-RAM disk 300 or a magneto-optical disk 240, a contentsprovider having, for example, a CATV station with the DVDrecording/reproduction apparatus shown in FIG. 14 or the magneto-opticalrecording/reproduction apparatus shown in FIG. 42 sends the scrambleddata, which has been encrypted with the ID number in the BCA as one key,to another recording/reproduction apparatus on the user side via acommunication line, and the scrambled data is temporarily recorded onthe DVD-RAM disk 300 a or magneto-optical disk 240 a of, for example,the CATV station. To reproduce the scrambled signal from the samemagneto-optical disk 240 a is authorized use, so that the BCA is read,and the signal is descrambled in a descrambling portion, that is, theencryption decoder 534 a, using the BCA data obtained from the BCAoutput portion 750 as the decryption key, as shown in FIG. 42. Then, theMPEG decoder 261 expands the MPEG signal to obtain the video signal. If,however, the scrambled data, that is recorded on the magneto-opticaldisk 240 a for authorized use, is copied onto a magneto-optical disk 240b, that is, unauthorized use is made, the correct decryption key fordescrambling the scrambled data cannot be obtained during reproduction,because the BCA data of the disks are different, so that the encryptiondecoder 534 a cannot descramble the signal. Therefore, the video signalcannot be output. Therefore, a signal that is illegally copied ontoanother magneto-optical disk 240 b cannot be reproduced, so that thecopyright can be protected. In effect, the contents can be recorded onand reproduced from only one magneto-optical disk 240 a. The same istrue for the DVD-RAM disk 300 a shown in FIG. 14, where the contentsalso can be recorded on and reproduced from only one disk.

[0248] The following is an explanation of an even tougher protectionmethod. First, the BCA data of the magneto-optical disk 240 on the userside are sent via communication line to the contents provider. Then, onthe contents provider side, the video signal is transmitted with the BCAdata buried inside the video signal as a watermark by the watermarkrecording portion 264. On the user side, this signal is recorded onto amagneto-optical disk 240 a. During reproduction, a watermarkreproduction verification portion 262 verifies the BCA data of therecording permission identifier and the watermark against the BCA dataobtained by the BCA output portion 750, and authorizes compoundreproduction only if they match. This makes the protection of copyrightseven stronger. Since with this method the watermark can be detected bythe watermark reproduction portion 263 even if a digital/analog copy istaken directly to video tape from the magneto-optical disk 240 a, theproduction of illegal digital copies can be prevented or detected. As inthe case of the DVD-RAM disk shown in FIG. 14, the production of illegaldigital copies can be prevented or detected.

[0249] In this case, by providing the magneto-opticalrecording/reproduction apparatus or the DVD recording/reproductionapparatus with a watermark reproduction portion 263, a recordingprevention portion 265 authorizes the recording only if there is awatermark indicating a “first recording possible identifier” in thesignal received from the contents provider. The recording preventionportion 265 and a “first recording completion identifier”, which isdiscussed below, prevent a second recording of the disk, that is,illegal copying. Moreover, an identifier showing “first recordingcompleted” and an individual disk number of the magneto-optical disk 240a pre-recorded in the BCA recording portion 220 are overlapped by thewatermark recording portion 264 with the recording signal with theprimary watermark and buried and recorded on the magneto-optical disk240 a as the second watermark. If the data from this magneto-optical 240a are descrambled or converted to analog and recorded onto other media,for example, a video tape or a DVD-RAM, then the “first recordingcompletion identifier” can be detected if the VTR or the like comprisesa watermark reproduction portion 263. Thus, the recording preventionportion 265 impedes the recording of a second tape or disk, so thatillegal copies are prevented. If the VTR is not equipped with awatermark production portion 263, an illegal copy can be produced.However, by examining the watermark of the illegally copied video tape,the recording history, for example, the name of the contents providercan be reproduced from the recording data of the primary watermark, andthe BCA disk ID of the first, legal recording can be reproduced from theburied secondary watermark, so that a follow-up check can be made fromwhich contents provider which (or whose) disk has been provided on whichdate. Consequently, the individual who broke the law can be identifiedand tried for copyright infringement, so that illegal copies and plansfor similar actions by the same infringer can be indirectly impeded.Since the watermark does not disappear even when converting the signalto analog, this is also useful for analog VTRs.

[0250] The following is an explanation of a recording apparatus that canrecord or transmit illegally by circumventing the copy protection eventhough a watermark indicating “first recording complete” or “recordingforbidden” is detected and by adding a circuit producing a scramblingkey. This case cannot be prevented directly, but the circumventioncircuit becomes extremely complicated. Moreover, as has been explainedabove, the recording history can be ascertained from the primary and thesecondary watermark, so that illegal copies and illegal use can beprevented indirectly, similar to the case explained above.

[0251] The following is an explanation of the particular effects of theBCA. The BCA data specify the disk, and with the BCA data the primaryuser of the contents, who is recorded in data base of the contentsprovider, can be specified. Therefore, by adding the BCA, the tracing ofillegal users becomes easy when watermarks are used.

[0252] Moreover, as is shown by the recording circuit 266 in FIGS. 14and 42, BCA data are used for a portion of the encryption key forscrambling, and for the primary watermark or the secondary watermark, sothat when both are checked for by the watermark reproduction portion 263of the reproduction apparatus, an even stronger copy protection can berealized.

[0253] Moreover, a watermark or scrambling key, to which a timeinformation input portion 269 has added the authorization dates fromsystem operators such as rental stores, is input into a scramblingportion 271, and synthesized into a password 271 a. When thereproduction device performs a verification of the date informationusing the password 271 a or the BCA data or the watermark, a periodwherein the scrambling key can be cancelled can be specified, forexample as “3 days use possible”, in the encryption decoder 534 a. Thisalso can be used for a rental disk system, which can be protected withthe copy prevention technology of the present invention, resulting instrong copyright protection and making illegal use very difficult.

[0254] As explained above, when the BCA is used for a rewritable opticaldisk, such as a magneto-optical disk used for an ASMO, the copyrightprotection through watermarks or scrambling can be strengthened evenfurther.

[0255] Moreover, the above embodiments have been explained for a DVD ROMdisk of two laminated disks, a RAM disk and a single-substrate opticaldisk. However, the present invention can be applied regardless of thedisk structure to any kind of disk with the same effect. In other words,recording the BCA on other types of ROM disks or RAM disks, on DVD-Rdisks, or magneto-optical disks, the same recording properties andreliability can be attained. The above explanations are equallyapplicable to DVD-R disks, DVD-RAM disks and magneto-optical disks, withthe same results, but these explanations have been omitted.

[0256] Moreover, the BCA identifying information in the aboveembodiments have the same information signal format for DVDs and formagneto-optical disks, so that using an optical head for magneto-opticaldisks with the structure in FIG. 7, the BCA identifying information forDVDs can be reproduced. And, in this case, an excellent reproductionsignal of the BCA identifying information with a small error rate can beattained with a reproduction filter and by adjusting the decodingconditions during reproduction.

[0257] Moreover, since in the magneto-optical disk of the aboveembodiments, only the magnetic properties of the recording layer arechanged, excellent reliability can be achieved in environmental tests,with no deterioration of the recording layer due to oxidation and nochange of the mechanical properties of the recording layer.

[0258] Furthermore, the above embodiments, have been explained by way ofexamples of a magneto-optical disk wherein the recording layer has athree-layer FAD structure. However, identifying information just aseasily can be recorded on a RAD type, a CAD type, or a double mask typemagneto-optical disk that can be reproduced with magnetically inducedsuper resolution, with a recording method of the above embodiments, sothat the copying of contents can be prevented, while maintainingexcellent detection signal properties.

[0259] Industrial Applicability

[0260] In accordance with the present invention identifying information(write-once information) easily can be recorded onto or reproduced fromoptical disks, the copying of contents can be prevented, which is usefulfor an apparatus for recording and reproducing optical disks with anaccent on copyright protection.

What is claimed is:
 1. An optical disk comprising: a disk substrate; anda recording layer on the disk substrate, the recording layer including amagnetic film with magnetic anisotropy in a direction perpendicular to asurface of the magnetic film; wherein the optical disk stores write-onceinformation formed by first recording areas and second recording areasin a pre-determined portion of said recording layer; a magneticanisotropy in a direction perpendicular to a surface of the secondrecording areas is smaller than a magnetic anisotropy in a directionperpendicular to a surface of the first recording areas; the secondrecording areas are formed as stripe-shaped marks that are oblong in aradial direction of the disk; and a plurality of the marks is arrangedin a circumferential direction of the disk, the arrangement being basedon a modulation signal of the write-once information.
 2. The opticaldisk according to claim 1 , further comprising an identifier forindication whether there is a row of a plurality of marks arranged in acircumferential direction of the disk.
 3. The optical disk according toclaim 2 , wherein the identifier indicating the row of marks is storedamong control data.
 4. The optical disk according to claim 1 , whereinthe pre-determined portion comprising write-once information is at aninner perimeter portion of the disk.
 5. The optical disk according toclaim 1 , wherein a difference between a luminous energy that isreflected from the first recording areas and a luminous energy that isreflected from the second recording areas is below a certain value. 6.The optical disk according to claim 5 , wherein the difference betweenluminous energy that is reflected from the first recording areas andluminous energy that is reflected from the second recording areas is notmore than 10%.
 7. The optical disk according to claim 1 , wherein adifference between an average refractive index of the first recordingareas and an average refractive index of the second recording areas isnot more than 5%.
 8. The optical disk according to claim 1 , wherein themagnetic anisotropy of the magnetic film of the second recording areasin an in-plane direction is dominant.
 9. The optical disk according toclaim 1 , wherein at least a portion of the magnetic film of the secondrecording areas is crystallized.
 10. The optical disk according to claim1 , wherein said recording layer comprises a multilayer magnetic film.11. An optical disk comprising: a disk substrate; and a recording layeron the disk substrate, the recording layer including a film that can bereversibly changed between two optically detectable states; wherein theoptical disk stores write-once information formed by first recordingareas and second recording areas in a pre-determined portion of saidrecording layer; a luminous energy that is reflected from the firstrecording areas differs from a luminous energy that is reflected fromthe second recording areas; the second recording areas are formed asstripe-shaped marks that are oblong in a radial direction of the disk;and a plurality of the marks is arranged in a circumferential directionof the disk, the arrangement being based on a modulation signal for thewrite-once information.
 12. The optical disk according to claim 11 ,further comprising an identifier for indication whether there is a rowof a plurality of marks arranged in a circumferential direction of thedisk.
 13. The optical disk according to claim 12 , wherein theidentifier indicating the row of marks is stored among control data. 14.The optical disk according to claim 11 , wherein the pre-determinedportion comprising write-once information is at an inner perimeterportion of the disk.
 15. The optical disk according to claim 11 ,wherein the recording layer undergoes a reversible phase change betweena crystalline phase and an amorphous phase, depending on irradiationconditions for irradiated light.
 16. The optical disk according to claim15 , wherein the difference between luminous energy that is reflectedfrom the first recording areas and luminous energy that is reflectedfrom the second recording areas is at least 10%.
 17. The optical diskaccording to claim 15 , wherein a difference between an averagerefractive index of the first recording areas and an average refractiveindex of the second recording areas is at least 5%.
 18. The optical diskaccording to claim 15 , wherein the second recording areas of saidrecording layer are in a crystalline phase.
 19. The optical diskaccording to claim 15 , wherein said recording layer comprises aGe—Sb—Te alloy.
 20. An optical disk whereon main information andwrite-once information is recorded, the write-once information beingdifferent for each disk, and the write-once information storing at leastwatermark production parameters for producing a watermark.
 21. Theoptical disk according to claim 20 , wherein the main information isrecorded by providing convex-concave pits in a reflective layer, and thewrite-once information is recorded by partially removing the reflectivelayer.
 22. The optical disk according to claim 20 , wherein the maininformation and the write-once information are recorded by partiallychanging a reflection coefficient of a reflective layer.
 23. The opticaldisk according to claim 20 , wherein a recording layer comprises amagnetic layer with a magnetic anisotropy in a direction perpendicularto a surface of the magnetic layer, the main information is recorded bypartially changing a magnetization direction of the recording layer, andthe write-once information is recorded by partially changing themagnetic anisotropy in the direction perpendicular to the surface of themagnetic layer.
 24. A method for recording write-once information ontoan optical disk (a) comprising a disk substrate, and a recording layeron the disk substrate, including a magnetic film with a magneticanisotropy in a direction perpendicular to a surface of the magneticfilm; and (b) storing write-once information formed by first recordingareas and second recording areas in a pre-determined portion of saidrecording layer; the method comprising forming the second recordingareas as a plurality of stripe-shaped marks that are oblong in a radialdirection of the disk in a circumferential direction of the disk byirradiating laser light based on a modulation signal of the write-onceinformation in a circumferential disk direction in the pre-determinedportion of said recording layer in a manner that a magnetic anisotropyin a direction perpendicular to a surface of the second recording areasbecomes smaller than a magnetic anisotropy in a direction perpendicularto a surface of the first recording areas.
 25. The recording methodaccording to claim 24 , wherein, when the second recording areas areformed, a laser light source is pulsed in accordance with a modulationsignal of phase-encoded write-once information, and the optical disk orthe laser light is rotated.
 26. The recording method according to claim24 , wherein the optical disk further comprises a reflective layer and aprotective layer on the disk substrate, and an intensity of laser lightirradiated to form the second recording areas is smaller than anintensity of laser light destroying at least one of the disk substrate,the reflective layer and the protective layer.
 27. The recording methodaccording to claim 24 , wherein an intensity of laser light irradiatedto form the second recording areas is an intensity for crystallizing atleast a portion of said recording layer.
 28. The recording methodaccording to claim 24 , wherein an intensity of laser light irradiatedto form the second recording areas is larger than an intensity of laserlight for heating said recording layer to a Curie temperature.
 29. Therecording method according to claim 24 , wherein an intensity of laserlight irradiated to form the second recording areas is an intensity formaking a magnetic anisotropy of the magnetic layer of the firstrecording areas in an in-plane direction dominant.
 30. The recordingmethod according to claim 24 , wherein, with a unidirectionalconvergence focusing lens, rectangularly stripe-shaped laser light isirradiated onto said recording layer when the second recording areas areformed.
 31. The recording method according to claim 24 , wherein a lightsource of the laser light that is irradiated for forming the secondrecording areas is a YAG laser.
 32. The recording method according toclaim 31 , wherein a magnetic field above a certain value is applied tosaid recording layer while irradiating laser light from the YAG laser.33. The recording method according to claim 32 , wherein the magneticfield applied to said recording layer is at least 5 kOe.
 34. A methodfor recording write-once information onto an optical disk (a) comprisinga disk substrate; and on the disk substrate a recording layer comprisinga film that can be reversibly changed between two optically detectablestates; and (b) storing write-once information formed by first recordingareas and second recording areas in a pre-determined portion of saidrecording layer; the method comprising forming the second recordingareas as a plurality of stripe-shaped marks that are oblong in a radialdirection of the disk in a circumferential direction of the disk byirradiating laser light based on a modulation signal of the write-onceinformation in a circumferential disk direction in the pre-determinedportion of said recording layer in a manner that a luminous energy oflight reflected from the first recording areas differs from a luminousenergy of light reflected from the second recording areas.
 35. Therecording method according to claim 34 , wherein, when the secondrecording areas are formed, a laser light source is pulsed in accordancewith a modulation signal of phase-encoded write-once information, andthe optical disk or the laser light is rotated.
 36. The recording methodaccording to claim 34 , wherein the optical disk further comprises areflective layer and a protective layer on the disk substrate, and anintensity of laser light irradiated to form the second recording areasis smaller than an intensity of laser light destroying at least one ofthe disk substrate, the reflective layer and the protective layer. 37.The recording method according to claim 34 , wherein an intensity oflaser light irradiated to form the second recording areas is anintensity for crystallizing at least a portion of said recording layer.38. The recording method according to claim 34 , wherein, with aunidirectional convergence focusing lens, rectangularly stripe-shapedlaser light is irradiated onto said recording layer when the secondrecording areas are formed.
 39. The recording method according to claim35 , wherein a light source of the laser light that is irradiated forforming the second recording areas is a YAG laser.
 40. A method forrecording write-once information onto an optical disk, comprising:producing a watermark based on a disk ID; and overlapping the watermarkon specific data to record it as write-once information.
 41. A methodfor reproducing write-once information from an optical disk (a)comprising a disk substrate, and a recording layer on the disksubstrate, the recording layer including a magnetic film with a magneticanisotropy in a direction perpendicular to a surface of the magneticfilm; and (b) storing write-once information formed by first recordingareas and second recording areas in a pre-determined portion of saidrecording layer, the first and second recording layers having differentmagnetic anisotropies in a direction perpendicular to a surface of themagnetic layer; the method comprising: irradiating linearly polarizedlaser light onto said pre-determined portion; and detecting a change ina polarization orientation of light reflected from the optical disk orlight transmitted through the optical disk.
 42. The reproducing methodaccording to claim 41 , wherein the linearly polarized laser light isirradiated onto said pre-determined portion after magnetizing therecording layer of said pre-determined portion in one step by applying amagnetic field that is larger than a coercive force of the recordinglayer in said pre-determined portion.
 43. The reproducing methodaccording to claim 41 , wherein the linearly polarized laser light isirradiated onto said pre-determined portion after aligning amagnetization of said recording layer of said pre-determined portion byapplying a unidirectional magnetic field to said pre-determined portionwhile increasing the temperature of said recording layer in saidpredetermined portion above the Curie temperature by irradiating laserlight of constant luminous energy.
 44. A method for reproducingwrite-once information from an optical disk (a) comprising a disksubstrate; and a recording layer on the disk substrate, the recordinglayer including a film that can be reversibly changed between twooptically detectable states; and (b) storing write-once informationformed by first recording areas and second recording areas withdifferent reflection coefficients in a pre-determined portion of saidrecording layer; the method comprising: irradiating focused laser lightonto said pre-determined portion; and detecting a change in a luminousenergy reflected from the disk.
 45. An apparatus for reproducing opticaldisks comprising (a) a main information recording area for recordingmain information; and (b) an auxiliary signal recording area overlappingpartly with the main information recording area for recording aphase-encoding modulated auxiliary signal that overlaps a signal of maininformation, the apparatus comprising: means for reproducing a maininformation signal in the main information recording area with anoptical head; first decoding means for decoding a main informationsignal to obtain main information data; means for reproducing a mixedsignal comprising a main information signal in said auxiliary signalrecording area and the auxiliary signal as a reproduction signal withthe optical head; frequency separation means for suppressing the maininformation signal in the reproduction signal to obtain the auxiliarysignal; and second decoding means for phase-encoding decoding theauxiliary signal to obtain the auxiliary data.
 46. The apparatusaccording to claim 45 , wherein the frequency separation means is alow-frequency component separation means for suppressing high frequencycomponents in the reproduction signal reproduced with the optical headto obtain a low frequency reproduction signal, the apparatus furthercomprises: a second-slice-level setting portion for producing a secondslice level from said low-frequency reproduction signal; and asecond-level slicer for slicing the low-frequency reproduction signal atthe second slice level to obtain a binarized signal; wherein theapparatus phase-encoding decodes the binarized signal to obtain theauxiliary data.
 47. The apparatus according to claim 46 , wherein thesecond-slice-level setting portion comprises auxiliary low-frequencycomponent separation means with a time constant that is larger than thatof the low-frequency component separation means; a reproduction signalreproduced with the optical head or a low-frequency reproduction signalobtained with the low-frequency component separation means is enteredinto the auxiliary low-frequency component separation means; andcomponents with frequencies lower than the low-frequency reproductionsignal are extracted to obtain a second slice level.
 48. The apparatusaccording to claim 45 , further comprising: frequency transformationmeans for transforming a main information signal included in areproduction signal reproduced with the optical head from a time domaininto a frequency domain to produce a first transformation signal; meansfor producing a mixed signal, wherein auxiliary information has beenadded or superposed to the first transformation signal; frequencyinverse-transformation means for transforming the mixed signal from thefrequency domain to the time domain to produce a second transformationsignal.
 49. An apparatus for reproducing optical disks, wherein anoptical head irradiates linearly polarized light onto an optical disk,and a change of a polarization orientation of light that is transmittedor reflected from the optical disk is detected in accordance with arecording signal on the optical disk; and the apparatus comprises: meansfor moving, when necessary, the optical head into a predeterminedportion of the optical disk where write-once information is stored, andmeans for reproducing the write-once information after detecting achange of a polarization orientation of light that is transmitted orreflected from the pre-determined portion.
 50. The apparatus accordingto claim 49 , further comprising means for detecting an identifierindicating whether write-once information within control data of theoptical disk is present, the indication being based on a detectionsignal of detection light that is received with at least onephotodetector of the optical head or on an all-sum signal of detectionsignals of detection light that is received with a plurality ofphoto-detectors of the optical head, wherein to detect the identifierand to verify whether write-once information is present, the opticalhead is moved to the pre-determined portion of the optical disk wherewrite-once information is stored, when necessary.
 51. The apparatusaccording to claim 49 , further comprising decoding means forphase-encoding decoding during reproduction of the write-onceinformation.
 52. An apparatus for reproducing optical disks whereon maininformation is stored and write-once information that differs for eachdisk is stored, the apparatus comprising: a signal reproduction portionfor reproducing the main information; a write-once informationreproduction portion for reproducing the write-once information; and awatermark attaching portion for producing a watermark signal based onthe write-once information, adding the watermark signal to the maininformation and giving it out.
 53. The apparatus according to claim 52 ,wherein the write-once information is recorded by partially changing areflection coefficient of a recording layer on the optical disk.
 54. Theapparatus according to claim 52 wherein a recording layer of the opticaldisk comprises a magnetic film having a magnetic anisotropy that isperpendicular to a film surface; and write-once information is stored bypartially changing the perpendicular magnetic anisotropy of the magneticfilm.
 55. The apparatus according to claim 52 wherein a watermarkattaching portion overlaps a signal of the main information withauxiliary information comprising a watermark.
 56. The apparatusaccording to claim 52 , further comprising: a frequency transformationmeans for producing a first transformation signal by transforming asignal of main information from a time domain into a frequency domain;means for producing a mixed signal by adding or superposing write-onceinformation and the first transformation signal; and frequencyinverse-transformation means for producing a second transformationsignal by transforming the mixed signal from the frequency domain intothe time domain.
 57. The apparatus according to claim 52 , furthercomprising: an MPEG decoder for expanding main information into a videosignal; and means for inputting the video signal into the watermarkattaching portion.
 58. The apparatus according to claim 57 , furthercomprising a watermark reproduction portion for reproducing watermarks;wherein said MPEG decoder and said watermark reproduction portion bothcomprise a mutual authentication portion; and encrypted main informationis sent and decrypted only if the mutual authentication portionsauthenticate each other.
 59. The apparatus according to claim 57 whereina decoded signal of main information that is compounded with anencryption decoder is input into the MPEG decoder.
 60. The apparatusaccording to claim 59 , further comprising a watermark reproductionportion for reproducing watermarks; wherein an encryption decoder andsaid watermark reproduction portion both comprise a mutualauthentication portion; and encrypted main information is sent anddecrypted only if the mutual authentication portions authenticate eachother.
 61. An apparatus for recording and reproducing optical diskswhereon information can be recorded, erased and reproduced and whereonmain information is stored on a main recording area of a recording layerof the optical disks using a recording circuit and an optical head, theapparatus comprising: means for reproducing write-once information, thatis recorded onto a pre-determined portion of the recording layer, usinga signal output portion of the optical head, which detects thewrite-once information as a change of a polarization orientation; meansfor recording the main information onto the main recording area asencrypted information that is encrypted with an encryption encoder usingthe write-once information; and means for reproducing the maininformation by reproducing the write-once information with the signaloutput portion of the optical head and decoding the encryptedinformation as a decryption key in an encryption decoder.
 62. Anapparatus for recording and reproducing optical disks whereon maininformation is recorded onto a main recording area of a recording layerof the optical disks using a recording circuit and an optical head, theapparatus comprising: a watermark attaching portion for adding awatermark to the main information; wherein write-once information thatis stored in a pre-determined portion of the recording layer isreproduced with the optical head; the reproduced write-once informationis added to the main information as a watermark with said watermarkattaching portion; the main information including the watermark isrecorded onto the main recording area.
 63. The apparatus according toclaim 62 , wherein the main information is recorded by partiallychanging a reflection coefficient of the recording layer.
 64. Theapparatus according to claim 62 wherein the recording layer comprises amagnetic film having a magnetic anisotropy that is perpendicular to afilm surface; and main information is stored by partially changing amagnetization direction of the magnetic film.
 65. The apparatusaccording to claim 64 wherein the main information and the write-onceinformation are reproduced by detecting a change of a magnetizationorientation of the recording layer or a change of the perpendicularanisotropy of the recording layer with an optical head as a change of apolarization orientation.
 66. The apparatus according to claim 62wherein a watermark attaching portion overlaps a signal of the maininformation with auxiliary information comprising a watermark.
 67. Theapparatus according to claim 62 , further comprising: a frequencytransformation means for producing a first transformation signal bytransforming a signal of main information from a time domain into afrequency domain; means for producing a mixed signal by adding orsuperposing write-once information and the first transformation signal;and frequency inverse-transformation means for producing a secondtransformation signal by transforming the mixed signal from thefrequency domain into the time domain.
 68. The apparatus according toclaim 62 , further comprising: an MPEG decoder for expanding maininformation into a video signal; and means for inputting the videosignal into the watermark attaching portion.
 69. The apparatus accordingto claim 68 , further comprising a watermark reproduction portion forreproducing watermarks; wherein said MPEG decoder and said watermarkreproduction portion both comprise a mutual authentication portion; andencrypted main information is sent and decrypted only if the mutualauthentication portions authenticate each other.
 70. The apparatusaccording to claim 68 wherein a decoded signal of main information thatis compounded with an encryption decoder is input into the MPEG decoder.71. The apparatus according to claim 70 , further comprising a watermarkreproduction portion for reproducing watermarks; wherein said encryptiondecoder and said watermark reproduction portion both comprise a mutualauthentication portion; and encrypted main information is sent anddecrypted only if the mutual authentication portions authenticate eachother.
 72. An apparatus for recording write-once information onto anoptical disk storing main information, the apparatus comprising meansfor recording auxiliary information comprising at least one of a disk IDand watermark production parameters.
 73. The apparatus according toclaim 72 , wherein the main information is stored by providingconvex-concave pits in a reflection film of the optical disk, and theauxiliary information is stored by partially erasing the reflectionfilm.
 74. The apparatus according to claim 72 , wherein the maininformation is stored by partially changing a reflection coefficient ofa recording layer of the optical disk, and the auxiliary information isstored by partially changing a reflection coefficient of the recordinglayer of the optical disk.
 75. The apparatus according to claim 72wherein a recording layer of the optical disk comprises a magnetic filmhaving a magnetic anisotropy that is perpendicular to a film surface;main information is stored by partially changing a magnetizationdirection of the magnetic film; and auxiliary information is stored bypartially changing the perpendicular magnetic anisotropy of the magneticfilm.
 76. An apparatus for recording optical disks storing maininformation, comprising: means for producing a watermark based onauxiliary information comprising a disk ID; and means for recordingdata, which consists of certain data to which the watermark has beensuperposed.